ドラフト ECMA-262 / 2025年7月24日
ECMAScript® 2026 言語仕様
この仕様について
https://tc39.es/ecma262/ のドキュメントは、最も正確で 最新の ECMAScript 仕様です。これは最新の年次スナップショットの内容に加え、スナップショット取得以降の 完了した提案 （提案プロセスで Stage 4 に達し、複数の実装で利用可能となり、次回の実際の改訂に含まれるもの）も含まれています。
このドキュメントは 単一ページ および 複数ページ で利用可能です。
この仕様への貢献について
この仕様は、ECMAScript コミュニティの協力のもと GitHub で開発されています。仕様の開発に貢献する方法はいくつかあります：
- GitHub リポジトリ: https://github.com/tc39/ecma262
- イシュー: 全イシュー, 新規イシューの作成
- プルリクエスト: 全プルリクエスト, 新規プルリクエストの作成
- テストスイート: Test262
- 編集者:
-
コミュニティ:
- Discourse: https://es.discourse.group/
- チャット: Matrix
- メーリング
リスト アーカイブ: https://esdiscuss.org/
このドキュメントの作成方法については
はじめに
このEcma規格は、ECMAScript 2026言語を定義します。これはECMAScript言語仕様の第17版です。1997年の初版発行以来、ECMAScriptは世界で最も広く使われている汎用プログラミング言語のひとつに成長しました。主にウェブブラウザに組み込まれている言語として知られていますが、サーバーや組み込みアプリケーションにも広く採用されています。
ECMAScriptは、主にJavaScript（Netscape）やJScript（Microsoft）など、いくつかの元技術に基づいています。この言語はBrendan EichによってNetscapeで発明され、同社のNavigator 2.0ブラウザで初めて登場しました。その後、Netscapeのすべてのブラウザと、MicrosoftのInternet Explorer 3.0以降のすべてのブラウザに実装されています。
ECMAScript言語仕様の開発は1996年11月に始まりました。このEcma規格の初版は、1997年6月のEcma総会で採択されました。
そのEcma規格はISO/IEC JTC 1に迅速な審査手続きで提出され、1998年4月に国際規格ISO/IEC 16262として承認されました。1998年6月のEcma総会では、ISO/IEC 16262と完全に一致させるため、ECMA-262第2版が承認されました。第1版と第2版の変更点は編集上のものです。
第3版では、強力な正規表現、より優れた文字列操作、新しい制御文、try/catch例外処理、エラー定義の厳格化、数値出力の書式指定、将来的な言語拡張を見据えた小規模な変更などが導入されました。ECMAScript標準の第3版は、1999年12月のEcma総会で採択され、2002年6月にISO/IEC 16262:2002として発行されました。
第3版発行後、ECMAScriptはWorld Wide Webとともに爆発的な普及を遂げ、ほぼすべてのウェブブラウザが対応するプログラミング言語となりました。第4版の開発も進みましたが、完成には至らず正式な第4版として発行されませんでした。ただし、その一部は第6版の開発に取り込まれています。
ECMAScript第5版（ECMA-262第5版として発行）は、ブラウザ実装で一般的となった言語仕様の事実上の解釈を明文化し、第3版発行以降に登場した新機能も追加しました。これらには、
第5版はISO/IEC JTC 1に迅速な審査手続きで提出され、国際規格ISO/IEC 16262:2011として承認されました。ECMAScript標準の第5.1版は細かな修正を取り入れており、ISO/IEC 16262:2011と同じ内容です。第5.1版は2011年6月のEcma総会で採択されました。
第6版の本格的な開発は2009年に始まりましたが、これは第3版（1999年発行）以降に行われてきたさまざまな実験や言語拡張設計の集大成です。この版の目標には、大規模アプリケーションやライブラリの開発、他言語のコンパイル先としてのECMAScript利用の強化が含まれていました。主な拡張としては、モジュール、クラス宣言、レキシカルブロックスコープ、
ECMAScript 2016は、Ecma TC39の新しい年次リリース体制と公開開発プロセスの下でリリースされた最初の版です。ECMAScript
2015のソースをプレーンテキストに変換した文書が、GitHub上での開発ベースとして使われました。この標準の開発期間中、数百件のプルリクエストやイシューが提出され、何千ものバグ修正、編集修正、その他の改善が行われました。また、Ecmarkup、Ecmarkdown、Grammarkdownなどのソフトウェアツールも開発されました。ES2016では新しいべき乗演算子やArray.prototypeのincludesメソッドが追加されました。
ECMAScript 2017では、Async Functions、Shared Memory、Atomicsの導入、その他小規模な言語・ライブラリの拡張、バグ修正、編集更新が行われました。Async
FunctionsはPromiseを返す関数のための構文を提供し、非同期プログラミング体験を向上させました。Shared
MemoryとAtomicsは、並列CPU上でも確定した実行順序を維持できる原子的操作を使って複数Object.values、Object.entries、Object.getOwnPropertyDescriptorsも追加されました。
ECMAScript 2018では、dotAllフラグ、名前付きキャプチャグループ、Unicodeプロパティエスケープ、後方参照）が追加され、オブジェクトのrest/spreadプロパティも追加されました。
ECMAScript
2019では、配列の平坦化のためのflatおよびflatMap（Array.prototype）、Object.entriesの戻り値を直接新しいオブジェクトに変換するObject.fromEntries、より適切な名称のtrimStartとtrimEnd（String.prototype、従来のtrimLeft/trimRightの代替）、その他細かな構文・意味論の更新が導入されました。構文の更新にはcatchバインディングパラメータの省略や、JSONとの整合性のために文字列リテラルでU+2028（LINE
SEPARATOR）とU+2029（PARAGRAPH
SEPARATOR）を許可することなどがあります。そのほか、Array.prototype.sortの安定化、JSON.stringifyのUTF-8出力標準化、Function.prototype.toStringの仕様明確化などが行われました。
ECMAScript
2020（第11版）では、グローバル正規表現による全マッチオブジェクトのイテレータを生成するmatchAllメソッド（Strings）、動的な指定子でモジュールを非同期インポートするimport()構文、任意精度整数用の新しい数値プリミティブBigInt、短絡しない新しいPromise合成手法Promise.allSettled、グローバルthis値への統一的アクセスglobalThis、モジュール内で使うexport * as ns from 'module'構文、for-in列挙順の標準化、モジュールに関するコンテキスト情報を持つimport.meta（
ECMAScript
2021（第12版）では、Strings用のreplaceAllメソッド、Promise合成のPromise.any（入力値のいずれかがfulfilledになると短絡）、複数のエラーを同時に表現する新しいError型AggregateError、論理代入演算子（??=、&&=、||=）、ガベージコレクションから保護せずにターゲットオブジェクトを参照するWeakRef、ターゲットオブジェクトのガベージコレクション時にクリーンアップ操作を管理するFinalizationRegistry、数値リテラルの区切り文字（1_000）、Array.prototype.sortの仕様厳密化（
ECMAScript 2022（第13版）では、モジュールのトップレベルでawaitを使えるようになり（#x in obj構文（オブジェクトのprivateフィールドの存在判定）、正規表現のマッチインデックス（/dフラグ）、Errorオブジェクトのcauseプロパティ（エラーの因果関係記録）、Strings/Arrays/atメソッド（相対インデックス）、Object.hasOwn（Object.prototype.hasOwnPropertyの便利な代替）などが導入されました。
ECMAScript
2023（第14版）では、Array.prototypeとTypedArray.prototypeにtoSorted、toReversed、with、findLast、findLastIndexが追加され、Array.prototypeにはtoSplicedが追加されました。また、実行可能なECMAScriptファイルのためにファイル先頭の#!コメント対応、ほとんどのSymbolをweakコレクションのキーとして利用可能になりました。
ECMAScript
2024（第15版）では、ArrayBufferやSharedArrayBufferのリサイズ・転送機能、文字列集合処理に便利な新しいRegExpの/vフラグ、Promise構築を容易にするPromise.withResolvers、データ集計用のObject.groupByおよびMap.groupBy、共有メモリの非同期変更待機用Atomics.waitAsync、Unicodeの正当性チェックと修正用String.prototype.isWellFormed・String.prototype.toWellFormedなどが追加されました。
ECMAScript 2025（第16版）では、イテレータ操作のための新しいグローバルIterator（Set.prototype用のセット操作メソッド、JSONモジュールのインポートとインポート属性宣言構文、正規表現で安全に使えるよう文字列エスケープするRegExp.escapeメソッド、正規表現修飾フラグのインライン制御構文、関数のPromise化のためのPromise.tryメソッド、そして新しいFloat16Array（DataView.prototype.getFloat16・DataView.prototype.setFloat16・Math.f16roundメソッドが追加されました。
Ecma TC39には多くの団体を代表する何十人もの個人が本版および過去の版の発展に大きく貢献しています。さらに、TC39のECMAScript活動を支える活発なコミュニティが生まれ、数多くのドラフトのレビュー、何千件ものバグ報告、実装実験、テストスイートの提供、世界中の開発者への教育が行われています。残念ながら、貢献者全員を特定し、記載することは不可能です。
Allen Wirfs-Brock
ECMA-262, プロジェクトエディター, 第6版
Brian Terlson
ECMA-262, プロジェクトエディター, 第7〜10版
Jordan Harband
ECMA-262, プロジェクトエディター, 第10〜12版
Shu-yu Guo
ECMA-262, プロジェクトエディター, 第12〜16版
Michael Ficarra
ECMA-262, プロジェクトエディター, 第12〜16版
Kevin Gibbons
ECMA-262, プロジェクトエディター, 第12〜16版
1 範囲
本規格はECMAScript 2026汎用プログラミング言語を定義します。
2 適合性
ECMAScriptの適合実装は、本仕様で記述されているすべての型、値、オブジェクト、プロパティ、関数、プログラム構文および意味論を提供し、サポートしなければなりません。
ECMAScriptの適合実装は、入力されたソーステキストをUnicode標準およびISO/IEC 10646の最新バージョンに準拠して解釈しなければなりません。
異なる言語や国の言語的・文化的慣習に適応するプログラムをサポートするアプリケーションプログラミングインターフェース（API）を提供するECMAScriptの適合実装は、本仕様と互換性のある最新のECMA-402版で定義されるインターフェースを実装しなければなりません。
ECMAScriptの適合実装は、本仕様で記述されている内容以外にも、追加の型、値、オブジェクト、プロパティ、関数を提供してもかまいません。特に、適合実装は本仕様で記載されていないプロパティや、そのプロパティの値を、本仕様で記述されているオブジェクトに対して提供してもかまいません。
ECMAScriptの適合実装は、本仕様で記載されていないプログラム構文や正規表現構文をサポートしてもかまいません。特に、適合実装は本仕様の
ECMAScriptの適合実装は、本仕様の
ECMAScriptの適合実装は、
ECMAScriptの適合実装は、規範的オプション（Normative Optional）サブ句を実装するかどうかを選択できます。規範的オプションの動作を実装する場合は、包含している規範的オプション句内のすべての動作を実装しなければなりません。規範的オプション句は、本仕様で「Normative Optional」と表示された色付きのボックスで示されます（下記参照）。
2.1 規範的オプション句の見出し例
句の内容例。
ECMAScriptの適合実装は、規範的オプションとしてもマークされていない限り、レガシー（Legacy）サブ句を実装しなければなりません。レガシーサブ句内で規定されている言語機能や動作には、ひとつ以上の望ましくない特徴がありますが、既存アプリケーションでの利用が継続されているため、本仕様から削除できません。これらの機能はECMAScript言語の中核部分とはみなされません。プログラマーは新しいECMAScriptコードを書く際、これらの機能や動作の利用や存在を前提にすべきではありません。
2.2 レガシー句の見出し例
句の内容例。
2.3 レガシー規範的オプション句の見出し例
句の内容例。
3 規範参照文献
以下の参照文書は、本書の適用に不可欠です。日付付き参照については、引用された版のみが適用されます。日付なし参照については、参照文書の最新版（改訂および修正を含む）が適用されます。
Unicode標準。
https://unicode.org/versions/latest
ISO/IEC 10646, 情報技術 ― ユニバーサル多オクテット符号化文字集合 (UCS) と改訂1:2005、改訂2:2006、改訂3:2008、改訂4:2008、追加改訂・正誤表、または後継。
ECMA-402, ECMAScript国際化API仕様、本仕様の版に対応する年次版。
https://www.ecma-international.org/publications-and-standards/standards/ecma-402/
ECMA-404, JSONデータ交換フォーマット。
https://www.ecma-international.org/publications-and-standards/standards/ecma-404/
4 概要
この節はECMAScript言語の非規範的な概要を含みます。
ECMAScriptは、
ECMAScriptは当初スクリプト言語として設計されましたが、現在では汎用プログラミング言語として広く使われています。スクリプト言語とは、既存システムの機能を操作・カスタマイズ・自動化するためのプログラミング言語です。こうしたシステムでは、ユーザーインターフェースを通じて有用な機能がすでに利用可能であり、スクリプト言語はその機能をプログラム制御に公開する手段となります。このように、既存システムはスクリプト言語の機能を補完する
ECMAScriptは当初Webスクリプト言語として設計され、ブラウザでWebページを動的にし、Webベースのクライアントサーバーアーキテクチャの一部としてサーバ計算を行う仕組みを提供していました。現在、ECMAScriptは様々な
ECMAScriptの利用は単純なスクリプトを超え、さまざまな環境や規模で多岐にわたるプログラミング業務に使われています。利用拡大に伴い、ECMAScriptが提供する機能や設備も拡充されました。現在、ECMAScriptは完全な機能を備えた汎用プログラミング言語となっています。
4.1 Webスクリプティング
ウェブブラウザは、クライアントサイド計算のためのECMAScript
ウェブサーバは、サーバサイド計算のための別の
ECMAScriptをサポートする各Webブラウザとサーバは、それぞれ独自の
4.2 ホストと実装
ECMAScriptを
実装は、付録
実装定義機能は、定義を外部ソースに委ねるものです。本仕様は特定の動作について推奨を行わず、適合実装は本仕様で定められた制約内で任意の動作を選択できます。
実装近似機能は、定義を外部ソースに委ねつつ、理想的な動作を推奨するものです。適合実装は制約内で任意の動作を選択できますが、理想的な動作に近づけることが奨励されます。例えば、Math.exp
ホストは、付録
ホストフックは、全体または一部が外部ソースで定義される抽象操作です。すべての
ホスト定義機能は、定義を外部ソースに委ねるもので、付録
ホスト環境は、すべての
本仕様は、常に最も具体的な用語を使う編集慣例に従います。例えば、機能が
4.3 ECMAScript概要
以下はECMAScriptの非公式な概要です。言語のすべての部分が説明されているわけではありません。この概要は規格本体の一部ではありません。
ECMAScriptはオブジェクトベースです。基本的な言語機能や
ECMAScriptは、ECMAScriptエンティティの定義を補完する組み込みオブジェクトの集合も定義します。これらの組み込みオブジェクトには、Object、Function、Boolean、Symbol、各種Errorオブジェクト、数値値の表現・操作用Math、Number、Date、テキスト処理用のString、RegExp、値のインデックス付きコレクションであるArrayと9種類のTyped
Array（要素が特定の数値データ表現を持つ）、キー付きコレクションのMap、Setオブジェクト、構造化データ用のJSONオブジェクト、ArrayBuffer、SharedArrayBuffer、DataView、制御抽象のためのジェネレータ関数やPromiseオブジェクト、リフレクション用のProxyやReflectなどが含まれます。
ECMAScriptは組み込み演算子も定義しています。ECMAScriptの演算子には、様々な単項演算、乗算演算子、加算演算子、ビットシフト演算子、関係演算子、等価演算子、2項ビット演算子、2項論理演算子、代入演算子、カンマ演算子などがあります。
大規模なECMAScriptプログラムはモジュールによってサポートされており、プログラムを複数の文や宣言の列に分割できます。各モジュールは、他のモジュールから提供される必要がある宣言、および他のモジュールで利用可能な自身の宣言を明示的に識別します。
ECMAScriptの構文は意図的にJavaの構文に似せてあります。ECMAScriptの構文は、使いやすいスクリプト言語として機能するよう緩和されています。例えば、変数は型宣言が不要であり、プロパティにも型は関連付けられず、定義された関数は呼び出しより前に宣言が現れている必要はありません。
4.3.1 オブジェクト
ECMAScriptはクラス定義の構文を含みますが、ECMAScriptオブジェクトはC++、Smalltalk、Javaのように本質的にクラスベースではありません。代わりに、オブジェクトはリテラル記法やnew Date(2009, 11)は新しいDateオブジェクトを生成します。newを使わずにDate()はオブジェクトではなく現在の日時の文字列を生成します。
クラスベースのオブジェクト指向言語では、一般に、状態はインスタンスが保持し、メソッドはクラスが保持し、継承は構造と振る舞いのみです。ECMAScriptでは、状態もメソッドもオブジェクトが保持し、構造・振る舞い・状態のすべてが継承されます。
プロトタイプが特定のプロパティを持っていて、そのプロパティを直接持たないすべてのオブジェクトは、そのプロパティと値を共有します。図1はこの関係を示しています。
CFはnew式で生成されています。各オブジェクトは
ほとんどのクラスベースオブジェクト言語と異なり、オブジェクトには値を代入することで動的にプロパティを追加できます。つまり、
ECMAScriptオブジェクトは本質的にクラスベースではありませんが、共通パターンの
4.3.2 ECMAScriptの厳格なバリアント
ECMAScript言語は、言語の一部機能の利用を制限したいユーザーがいる可能性を認識しています。これは、セキュリティの観点、エラーを招きやすい機能の回避、エラー検出の強化、その他ユーザー独自の理由によるものです。この可能性をサポートするために、ECMAScriptは言語の厳格なバリアントを定義しています。厳格なバリアントでは、通常のECMAScript言語から特定の構文的・意味的機能を除外し、一部機能の詳細な意味論を変更します。厳格なバリアントでは、非厳格な言語形式ではエラーとされない状況でも、エラー例外をthrowして報告しなければならない追加のエラー条件も規定しています。
ECMAScriptの厳格なバリアントは、一般に言語のstrict mode（厳格モード）と呼ばれます。厳格モードの選択と構文・意味論の利用は、
本仕様に適合するために、ECMAScriptの実装は本仕様で定義された完全な非制限ECMAScript言語と厳格なバリアントの両方を実装しなければなりません。さらに、非制限モードと厳格モードのソーステキストユニットの組み合わせによる複合プログラムもサポートしなければなりません。
4.4 用語と定義
本書の目的において、以下の用語と定義が適用されます。
4.4.1 implementation-approximated
4.4.2 implementation-defined
4.4.3 host-defined
編集上の観点では、
4.4.4 type
4.4.5 primitive value
型 Undefined、Null、Boolean、Number、BigInt、Symbol、String のいずれかのメンバー（
プリミティブ値は、言語実装の最下層レベルで直接表現されるデータです。
4.4.6 object
型 Object のメンバー
オブジェクトはプロパティの集合体であり、単一のプロトタイプオブジェクトを持ちます。プロトタイプは
4.4.7 constructor
オブジェクトを生成・初期化する
4.4.8 prototype
他のオブジェクトに共有プロパティを提供するオブジェクト
constructor.prototype
で参照でき、プロトタイプに追加されたプロパティは継承によりそのプロトタイプを共有するすべてのオブジェクトで共有されます。あるいは、Object.create
組み込み関数を使って明示的に指定したプロトタイプ付きの新しいオブジェクトを生成することもできます。
4.4.9 ordinary object
すべてのオブジェクトがサポートすべき本質的な内部メソッドに対してデフォルトの動作を持つオブジェクト
4.4.10 exotic object
本質的な内部メソッドのうち1つ以上についてデフォルトの動作を持たないオブジェクト
4.4.11 standard object
本仕様で意味論が定義されているオブジェクト
4.4.12 built-in object
ECMAScript実装によって規定・提供されるオブジェクト
標準の組み込みオブジェクトは本仕様で定義されています。ECMAScript実装は追加の組み込みオブジェクトを規定・提供してもかまいません。
4.4.13 undefined value
変数に値が代入されていない場合に使われるプリミティブ値
4.4.14 Undefined type
唯一の値が
4.4.15 null value
いかなるオブジェクト値も意図的に存在しないことを表すプリミティブ値
4.4.16 Null type
唯一の値が
4.4.17 Boolean value
Boolean値は
4.4.18 Boolean type
プリミティブ値
4.4.19 Boolean object
標準組み込み Boolean
Booleanオブジェクトは、Boolean new
式で使い、Boolean値を引数として生成されます。生成されたオブジェクトは内部スロットにBoolean値を保持します。BooleanオブジェクトはBoolean値に強制変換することができます。
4.4.20 String value
ゼロ以上の16ビット符号なし
String値は
4.4.21 String type
すべての可能なString値の集合
4.4.22 String object
標準組み込み String
Stringオブジェクトは、String new
式で使い、String値を引数として生成されます。生成されたオブジェクトは内部スロットにString値を保持します。Stringオブジェクトは、String
4.4.23 Number value
倍精度64ビットバイナリ形式
Number値は
4.4.24 Number type
すべての可能なNumber値の集合（
4.4.25 Number object
標準組み込み Number
Numberオブジェクトは、Number new
式で使い、Number値を引数として生成されます。生成されたオブジェクトは内部スロットにNumber値を保持します。Numberオブジェクトは、Number
4.4.26 Infinity
正の無限大のNumber値
4.4.27 NaN
4.4.28 BigInt value
任意精度
4.4.29 BigInt type
すべての可能なBigInt値の集合
4.4.30 BigInt object
標準組み込み BigInt
4.4.31 Symbol value
ユニークな、非Stringオブジェクト
4.4.32 Symbol type
すべての可能なSymbol値の集合
4.4.33 Symbol object
標準組み込み Symbol
4.4.34 function
サブルーチンとして呼び出すことができる
関数はプロパティに加え、呼び出されたときの挙動を決定する実行コードと状態を持ちます。関数のコードはECMAScriptで記述されている場合とそうでない場合があります。
4.4.35 built-in function
関数である組み込みオブジェクト
組み込み関数の例：parseInt、Math.exp。
4.4.36 built-in constructor
組み込み Object、Function。
4.4.37 property
キー（String値またはSymbol値）と値を関連付けるオブジェクトの一部
プロパティの形態によって、値はデータ値（プリミティブ値、オブジェクト、
4.4.38 method
プロパティの値である関数
関数がオブジェクトのメソッドとして呼び出されると、そのオブジェクトは関数に
4.4.39 built-in method
組み込み関数であるメソッド
標準組み込みメソッドは本仕様で定義されています。
4.4.40 attribute
プロパティの特徴を定義する内部値
4.4.41 own property
オブジェクトが直接保持するプロパティ
4.4.42 inherited property
オブジェクト自身のプロパティではないが、そのオブジェクトのプロトタイプの（自身または継承された）プロパティであるプロパティ
4.5 本仕様書の構成
本仕様書の残りの部分は以下のように構成されています：
第
第
第
第
第
5 記法上の規則
5.1 構文および字句文法
5.1.1 文脈自由文法
文脈自由文法は複数の生成規則から成ります。各生成規則は、非終端記号と呼ばれる抽象記号を左辺とし、0個以上の非終端記号および終端記号記号から成る列を右辺とします。各文法において、終端記号は特定のアルファベットから選ばれます。
連鎖生成規則は、右辺にちょうど1つの非終端記号と0個以上の終端記号を持つ生成規則です。
特別な非終端記号（目標記号）のみから成る文を始点として、与えられた文脈自由文法は言語を規定します。つまり、非終端記号を対応する左辺を持つ生成規則の右辺へ繰り返し置換することで得られる終端記号の可能な（無限かもしれない）列の集合です。
5.1.2 字句文法と正規表現文法
ECMAScriptの字句文法は、
空白やコメント以外の入力要素が、ECMAScriptの構文文法の終端記号となり、ECMAScriptのトークンと呼ばれます。これらのトークンは、/*…*/形式のコメント）は、行終端子を含まなければ単純に破棄されますが、行終端子を1つ以上含む場合は、1つの行終端子に置換され、構文文法の入力要素列に含まれます。
ECMAScriptの正規表現文法は
字句文法と正規表現文法の生成規則は、区切り記号として二重コロン“::”を用いて区別されます。字句文法と正規表現文法は、いくつかの生成規則を共有します。
5.1.3 数値文字列文法
数値文字列文法は
数値文字列文法の生成規則は、三重コロン“:::”を区切り記号として区別され、ソーステキストの解析には決して使用されません。
5.1.4 構文文法
ECMAScriptの構文文法は、
コードポイントの列をECMAScriptの
解析が成功すると、構文木（根付き木構造）が構築されます。各ノードは構文ノードです。各構文ノードは文法記号のインスタンスであり、その記号から導出可能なソーステキストの範囲を表します。構文木の根ノード（ソーステキスト全体を表す）は、解析の
新しい構文ノードはパーサーの各呼び出しごとにインスタンス化され、同一ソーステキストであっても解析間で再利用されることはありません。構文ノードは、同じソーステキスト範囲を表し、同じ文法記号のインスタンスであり、同じパーサー呼び出しから生成された場合のみ同じ構文ノードとみなされます。
同じ文字列を複数回解析すると、異なる構文ノードが得られます。例えば、次のようになります：
let str = "1 + 1;";
eval(str);
eval(str);各evalの呼び出しは、strの値を
構文文法の生成規則は、区切り記号として単一コロン“:”を用いて区別されます。
曖昧さを避けるために、構文文法では時折拡張生成規則を用いて、ECMAScriptの
- Pが元々マッチしたトークン列を、Nを
目標記号 として再度解析します。Nが文法パラメータを持つ場合、Pを元々解析したときと同じ値に設定します。 - そのトークン列が、余分なトークンなく単一のNインスタンスとして解析できれば：
- そのPに対して一意となるNのインスタンス（構文ノード）を「PがカバーするN」と呼びます。
- Nおよび派生生成規則の全ての早期エラー規則は、PがカバーするNにも適用されます。
- そうでなければ（解析に失敗した場合）、早期構文エラーとなります。
5.1.5 文法記法
5.1.5.1 終端記号
ECMAScriptの文法では、一部の終端記号が固定幅フォントで表示されています。これらはソーステキストに記載されたとおりに正確に現れる必要があります。この方法で指定されたすべての終端記号コードポイントは、他のUnicode範囲に類似したコードポイントではなく、Basic
Latinブロックの適切なUnicodeコードポイントとみなされます。終端記号内のコードポイントは、\
終端記号が個々のUnicodeコードポイントである文法（すなわち字句文法、正規表現文法、数値文字列文法）では、生成規則に複数の固定幅コードポイントが連続して現れる場合、それは同じコードポイント列を個別の終端記号として記載する場合の省略記法です。
例えば、次の生成規則：
は次の省略記法です：
対照的に、構文文法では固定幅コードポイントの連続は１つの終端記号となります。
終端記号には他にも2つの形式があります：
- 字句文法と正規表現文法では、通常の印刷表現がないUnicodeコードポイントは「<ABBREV>」の形式で示されます。ここで「ABBREV」はコードポイントまたはコードポイントの集合の記憶語です。これらの形式は
Unicode書式制御文字 、空白 、および行終端子 で定義されています。 - 構文文法では、特定の終端記号（例：
IdentifierName やRegularExpressionLiteral ）はイタリック体で表示されます。これは字句文法の同名の非終端記号を参照することを示します。
5.1.5.2 非終端記号と生成規則
非終端記号はイタリック体で表示されます。非終端記号（「生成規則」とも呼ばれる）の定義は、定義される非終端記号の名前の後にコロンが1つ以上続いて導入されます（コロンの数は生成規則が属する文法を示します）。続く行に、その非終端記号の右辺の選択肢が1つ以上続きます。例えば、次の構文定義：
は、非終端記号whileトークン、左括弧トークン、
は、
5.1.5.3 オプション記号
終端記号または非終端記号の後に付く下付き接尾辞「opt」は、オプション記号を示します。オプション記号を含む選択肢は、オプション要素を省略する右辺と含める右辺の2つを実際に指定します。これはつまり：
は次の省略記法です：
また：
は次の省略記法です：
さらに次の省略記法となります：
したがって、この例では非終端記号
5.1.5.4 文法パラメータ
生成規則は「[parameters]」という下付き注釈でパラメータ化できます。これは、生成規則で定義される非終端記号の記号の後ろに接尾辞として現れます。「parameters」は名前1つまたはカンマ区切りの名前リストです。パラメータ化された生成規則は、パラメータ名全組み合わせを定義する一連の生成規則の省略記法です。これはつまり：
は次の省略記法です：
また：
は次の省略記法です：
複数パラメータの場合、生成規則の組み合わせ数は組み合わせ的に増えますが、すべてが完全な文法で参照されるとは限りません。
生成規則右辺で非終端記号への参照もパラメータ化できます。例えば：
は次の意味です：
また：
は次の意味です：
非終端記号参照はパラメータリストと「opt」接尾辞の両方を持つことができます。例えば：
は次の省略記法です：
右辺の非終端記号参照に「?」を付けると、そのパラメータ値は現在の生成規則左辺記号の該当パラメータの有無によって決まります。例えば：
は次の省略記法です：
右辺選択肢が「[+parameter]」で始まる場合、その選択肢は指定したパラメータが該当生成規則非終端記号参照で使用されている場合のみ利用できます。「[~parameter]」で始まる場合は参照にそのパラメータが使われていない場合のみ利用できます。これはつまり：
は次の省略記法です：
また：
は次の省略記法です：
5.1.5.5 one of
文法定義でコロンの後に「one of」が続く場合、続く行に現れる各終端記号が選択肢となることを示します。例えば、ECMAScriptの字句文法には次の生成規則があります：
これは次の省略記法です：
5.1.5.6 [empty]
生成規則の右辺に「[empty]」と記載されている場合、その生成規則の右辺には終端記号や非終端記号が含まれていないことを示します。
5.1.5.7 先読み制限
生成規則の右辺に「[lookahead =
seq]」が現れる場合、その生成規則は直後の入力トークン列の先頭がseqである場合のみ使用可能であることを示します。同様に「[lookahead
∈ set]」（setは
これらの条件は否定も可能です。「[lookahead ≠ seq]」はseqが直後の入力トークン列の先頭ではない場合のみ使用可能、「[lookahead ∉ set]」はsetのいずれも直後のトークン列先頭でない場合のみ使用可能です。
例として、次の定義の場合：
次の定義：
は、「n」の後に1つ以上の10進数字が続き、その先頭が偶数である場合、または10進数字がさらに続かない場合に一致します。
これらの表現が構文文法で使われる場合、直後のトークン列を一意に特定できない場合があります。これは、後続トークンを特定するには後の位置でどの字句
5.1.5.8 [no LineTerminator here]
構文文法の生成規則右辺に「[no
は、スクリプト内でthrowトークンと
制限付き生成規則で
5.1.5.9 but not
生成規則右辺で「but not」を使い、除外する展開を指定することができます。例えば次の生成規則：
は、非終端記号
5.1.5.10 説明的表現
最後に、選択肢をすべて列挙するのが非現実的な場合に限り、いくつかの非終端記号はサンセリフ体の説明的表現で記述されています：
5.2 アルゴリズム規約
この仕様書では、アルゴリズムの手順を指定するために番号付きリストを頻繁に使用します。これらのアルゴリズムは、ECMAScript言語構造の必要な意味論を正確に規定するために使われます。アルゴリズムは特定の実装技法の使用を示唆するものではありません。実際には、与えられた機能を実装するために、より効率的なアルゴリズムが利用可能な場合があります。
アルゴリズムは、順序付き・カンマ区切りの別名（エイリアス）名の列で明示的にパラメータ化される場合があります。これらはアルゴリズムの手順内で、その位置に渡された引数を参照するために使われます。オプションのパラメータは角括弧（[
, name ]）で囲んで表し、アルゴリズム手順内では必須のパラメータと同じ扱いになります。残余パラメータはパラメータリストの末尾に「...」を付けて（,
...name）表し、必須・オプションパラメータの後に渡されたすべての引数を
アルゴリズムの手順は、さらに順序付きのサブステップに分割できます。サブステップはインデントで示され、さらにインデントされたサブステップに分割できます。段階番号付け規則により、最初のレベルは英小文字、2番目はローマ小文字、3レベル以上は4番目以降で数字ラベルが使われます。例えば：
- 最上位の手順
- サブステップ。
- サブステップ。
- サブサブステップ。
- サブサブサブステップ
- サブサブサブサブステップ
- サブサブサブサブサブステップ
- サブサブサブサブステップ
- サブサブサブステップ
- サブサブステップ。
手順やサブステップは「if」条件文として記述でき、その場合サブステップは条件が真の時のみ適用されます。同じレベルの「if」条件文の次に「else」で始まる手順やサブステップは、その条件の否定です。
手順では、サブステップの反復適用を指定することもできます。
「Assert:」で始まる手順は、そのアルゴリズムの不変条件を主張します。これらの主張は、暗黙的なアルゴリズムの不変条件を明示するためのものであり、追加の意味論的要件を加えるものではなく、実装で検証する必要はありません。単にアルゴリズムの明確化のために用いられます。
アルゴリズムの手順では「Let x be someValue」の形式で値に名前付きエイリアスを宣言できます。これらのエイリアスは参照的であり、xとsomeValueは同じデータを参照し、どちらかの変更は双方に反映されます。参照的動作を避けたい場合は、手順内で「Let x be a copy of someValue」のように右辺のコピーを明示的に作成する必要があります。
宣言されたエイリアスは、その後の手順で参照できますが、宣言前の手順で参照してはなりません。エイリアスは「Set x to someOtherValue」の形式で変更できます。
5.2.1 抽象操作
この仕様の複数箇所で使用できるように、いくつかのアルゴリズムは抽象操作と呼ばれ、パラメータ化された関数形式で名前付き定義され、他のアルゴリズムから名前で参照できるようになっています。抽象操作は通常、OperationName(arg1, arg2)のような関数適用形式で参照されます。一部の抽象操作は、クラス的な仕様抽象の多態的にディスパッチされるメソッドとして扱われます。そのようなメソッド的抽象操作は、someValue.OperationName(arg1, arg2)のように参照されます。
5.2.2 構文指向操作
構文指向操作は、名前付き操作であり、その定義はECMAScript文法の生成規則（複数の選択肢がある場合はそれぞれ）に関連付けられたアルゴリズムから成ります。複数の選択肢がある生成規則には通常、各選択肢ごとに別個のアルゴリズムがあります。アルゴリズムが文法生成規則に関連付けられる場合、生成規則の終端記号および非終端記号は、アルゴリズムのパラメータのように参照できます。この際、非終端記号は、ソーステキストを解析した際に一致した実際の選択肢定義を参照します。文法生成規則やそれから派生した
生成規則選択肢に関連付けられたアルゴリズムは、通常「[ ]」などの文法注釈なしで示されます。これらの注釈は構文的認識にのみ影響し、選択肢の意味論には影響しません。
構文指向操作は、構文ノードおよび必要に応じて他のパラメータを受けて、以下のアルゴリズムの
- Let status be SyntaxDirectedOperation of
SomeNonTerminal . - Let someParseNode be the parse of some source text.
- Perform SyntaxDirectedOperation of someParseNode.
- Perform SyntaxDirectedOperation of
someParseNode with argument
"value" .
明示的に指定されない限り、すべての
しかし、
実行時意味論:
- Return
Evaluation ofStatementList .
5.2.3 実行時意味論
実行時に呼び出される必要のある意味論を規定するアルゴリズムは実行時意味論と呼ばれます。実行時意味論は
5.2.3.1 Completion ( completionRecord )
抽象操作Completionは、引数completionRecord（
Assert : completionRecordはCompletion Record である。- completionRecordを返す。
5.2.3.2 例外を投げる
「例外を投げる」と記載されたアルゴリズム手順（例）：
- TypeError例外を投げる。
は次の記述と同じ意味です：
- 新しく作成したTypeErrorオブジェクトで
ThrowCompletion を返す。
5.2.3.3 ReturnIfAbrupt
「
ReturnIfAbrupt (argument)。
は次の意味です：
Assert : argumentはCompletion Record である。- もしargumentが
abrupt completion なら、Completion (argument)を返す。 - それ以外は、argumentをargument.[[Value]]に設定する。
また、「
- Let hygienicTemp be AbstractOperation()。
Assert : hygienicTempはCompletion Record である。- もしhygienicTempが
abrupt completion なら、Completion (hygienicTemp)を返す。 - それ以外は、hygienicTempをhygienicTemp.[[Value]]に設定する。
ここでhygienicTempはReturnIfAbruptに関する手順内のみ一時的に有効です。
また、「Let result be AbstractOperation(
Assert : argumentはCompletion Record である。- もしargumentが
abrupt completion なら、Completion (argument)を返す。 - それ以外は、argumentをargument.[[Value]]に設定する。
- Let result be AbstractOperation(argument)。
5.2.3.4 ReturnIfAbruptの省略記法
?を付けることで、結果の
- ? OperationName()。
は次の手順と同じ意味です：
ReturnIfAbrupt (OperationName())。
同様に、メソッド呼び出し形式の場合：
- ? someValue.OperationName()。
は次の意味です：
ReturnIfAbrupt (someValue.OperationName())。
また、!を前置することで、抽象操作や
- Let val be ! OperationName()。
は次の手順と同じ意味です：
- Let val be OperationName()。
Assert : valはnormal completion である。- valをval.[[Value]]に設定する。
!または?を付けます：
- Perform ! SyntaxDirectedOperation of
NonTerminal 。
5.2.3.5 暗黙的な通常完了
Completion 、NormalCompletion 、ThrowCompletion 、ReturnCompletion の結果を直接返す場合Completion Record の生成結果を直接返す場合
それ以外の方法で
- Return
true 。
は次のいずれとも同じ意味です：
- Return
NormalCompletion (true )。
または
- Let completion be
NormalCompletion (true )。 - Return
Completion (completion)。
または
- Return
Completion Record { [[Type]]:normal , [[Value]]:true , [[Target]]:empty }。
- Return ? completion。
次の例は編集上の誤りです。なぜなら
- Let completion be
NormalCompletion (true )。 - Return completion。
5.2.4 静的意味論
文脈自由文法だけでは、入力要素列が評価可能な有効なECMAScript
静的意味論規則は名前を持ち、通常アルゴリズムで定義されます。名前付き静的意味論規則は文法生成規則に関連付けられ、複数の選択肢がある生成規則には通常、各選択肢ごと・各適用規則ごとに別個のアルゴリズムが定義されます。
静的意味論規則の特例として早期エラー規則があります。
5.2.5 数学演算
この仕様書では、次の種類の数値値を参照します：
- 数学値: 任意の実数で、既定の数値型です。
- 拡張数学値:
数学値 に加え、+∞と-∞を含みます。 - Numbers:
IEEE 754-2019 binary64（倍精度浮動小数点）値です。 - BigInts:
ECMAScript言語値 で、任意の整数 と一対一で対応します。
この仕様書では、数値値の種類を下付き接尾辞で区別します。下付き𝔽はNumbersを、下付きℤはBigIntsを指します。下付き接尾辞のない数値値は
この仕様書で数値値について言及する場合（例：「yの長さ」や「4つの16進数字で表される
この仕様書で整数という用語が使われる場合、特に断りがなければ、
+, ×, =, ≥などの数値演算子は、オペランドの型ごとに対応する演算を指します。
数学関数
数学関数
記法「
「clamping x between lower and upper」とは、xがlower未満ならlower、upperより大きければupper、それ以外はx自身を返します（lowerとupperは数学値でlower ≤ upper）。
数学関数
数学関数
数学関数
区間は、下限aから上限bまでの、同じ数値型の値の集合（無限・空の場合もありえます）です。各境界は包含か非包含かが示されます。区間には次の4種があります：
- 下限a（含む）から上限b（含む）の区間（包含区間）は、a ≤ x ≤ bを満たすすべてのxのみ含みます。
- 下限a（含む）から上限b（含まない）の区間は、a ≤ x < bを満たすxのみ含みます。
- 下限a（含まない）から上限b（含む）の区間は、a < x ≤ bを満たすxのみ含みます。
- 下限a（含まない）から上限b（含まない）の区間は、a < x < bを満たすxのみ含みます。
例えば、下限1（含む）から上限2（含まない）の区間は、1以上2未満のすべての
5.2.6 値記法
この仕様書では、Function.prototype.applyやlet n = 42;）とは区別されます。
5.2.7 同一性
この仕様書では、仕様値と
この仕様書の観点では、「is」は2つの値の等価性比較（例：「If bool is
ECMAScript言語の観点では、言語値は
仕様値の例として、同一性のない値には、
仕様上の同一性は、Symbol値（
6 ECMAScriptのデータ型と値
この仕様のアルゴリズムは、型が関連付けられた値を操作します。値の型は、まさにこの節で定義されているものだけです。型はさらに
6.1 ECMAScript言語型
ECMAScript言語型は、ECMAScriptプログラマがECMAScript言語で直接操作する値に対応します。ECMAScript言語型は、Undefined、Null、Boolean、String、Symbol、Number、BigInt、Objectです。ECMAScript言語値は、ECMAScript言語型で特徴付けられる値です。
6.1.1 Undefined型
Undefined型は、
6.1.2 Null型
Null型は、
6.1.3 Boolean型
Boolean型は、
6.1.4 String型
String型は、最大長253-1要素までの、0個以上の16ビット符号なし
String内容を解釈しないECMAScript操作は、これ以上意味論を与えません。String値を解釈する操作は、各要素を単一のUTF-16コード単位として扱います。ただし、ECMAScriptはこれらのコード単位の値や関係性を制限しないため、さらにString内容をUTF-16で符号化されたUnicodeコードポイントの列として解釈する操作は、不正な部分列を考慮する必要があります。こうした操作は、数値値が
-
コード単位が
リーディングサロゲート でもトレーリングサロゲート でもなければ、その値を持つコードポイントとして解釈されます。 -
2つのコード単位の並びで、最初のコード単位c1が
リーディングサロゲート 、2番目c2がトレーリングサロゲート なら、それはサロゲートペアであり、コードポイント値は(c1 - 0xD800) × 0x400 + (c2 - 0xDC00) + 0x10000となります。（11.1.3 参照） -
コード単位が
リーディングサロゲート またはトレーリングサロゲート であっても、サロゲートペア の一部でない場合は、その値を持つコードポイントとして解釈されます。
関数String.prototype.normalize（String.prototype.localeCompare（
この設計の理由は、Stringの実装を可能な限り単純かつ高性能に保つことにありました。
この仕様では、「string-concatenation of A, B, ...」という表現（各引数はString値、コード単位、またはコード単位の列）は、それぞれの引数（順番通り）のコード単位列を連結したString値を指します。
「substring of S from inclusiveStart
to
exclusiveEnd」という表現（SはString値またはコード単位の列、inclusiveStartとexclusiveEndは
この仕様の「ASCIIワード文字」は、Unicode Basic
Latinブロックのすべての文字と数字、およびU+005F（LOW LINE）だけからなる次のString値を指します：
歴史的理由により、いくつかのアルゴリズムで重要な意味を持ちます。
6.1.4.1 StringIndexOf ( string, searchValue, fromIndex )
抽象操作StringIndexOfは、引数string（String）、searchValue（String）、fromIndex（非負の
searchValueが空文字列かつfromIndex ≤ stringの長さなら、このアルゴリズムはfromIndexを返します。空文字列は文字列内のすべての位置（最後のコード単位の後も含む）で見つかったものとみなされます。
fromIndex +
searchValueの長さがstringの長さを超える場合、このアルゴリズムは常に
6.1.4.2 StringLastIndexOf ( string, searchValue, fromIndex )
抽象操作StringLastIndexOfは、引数string（String）、searchValue（String）、fromIndex（非負の
searchValueが空文字列の場合、このアルゴリズムはfromIndexを返します。空文字列は文字列内のすべての位置（最後のコード単位の後も含む）で見つかったものとみなされます。
6.1.5 Symbol型
Symbol型は、Objectプロパティのキーとして使用できるすべての非String値の集合です（
Symbol値はそれぞれ一意かつ不変です。
各Symbol値は、
6.1.5.1 既知のSymbol
既知のSymbolは、この仕様のアルゴリズムで明示的に参照される組み込みのSymbol値です。これらは通常、仕様アルゴリズムの拡張ポイントとなる値を持つプロパティのキーとして使用されます。特に規定がなければ、既知のSymbol値はすべての
この仕様書では、既知のSymbolは標準の
%Symbol.name%が使われます。特に次の名前が使われていました：@@asyncIterator、@@hasInstance、@@isConcatSpreadable、@@| 仕様名 | [[Description]] | 値と目的 |
|---|---|---|
| %Symbol.asyncIterator% |
|
オブジェクトのデフォルトのfor-await-of文の意味論で呼び出されます。
|
| %Symbol.hasInstance% |
|
instanceof演算子の意味論で呼び出されます。
|
| %Symbol.isConcatSpreadable% |
|
この値がtrueなら、Array.prototype.concat |
| %Symbol.iterator% |
|
オブジェクトのデフォルトの |
| %Symbol.match% |
|
正規表現メソッドで、正規表現を文字列に対してマッチさせます。String.prototype.match |
| %Symbol.matchAll% |
|
正規表現メソッドで、文字列に対してマッチした結果を返すString.prototype.matchAll |
| %Symbol.replace% |
|
正規表現メソッドで、文字列の一致部分を置換します。String.prototype.replace |
| %Symbol.search% |
|
正規表現メソッドで、文字列内で正規表現に一致するインデックスを返します。String.prototype.search |
| %Symbol.species% |
|
派生オブジェクトの生成に使われる |
| %Symbol.split% |
|
正規表現メソッドで、正規表現に一致するインデックスで文字列を分割します。String.prototype.split |
| %Symbol.toPrimitive% |
|
オブジェクトを対応するプリミティブ値に変換するメソッド。 |
| %Symbol.toStringTag% |
|
オブジェクトのデフォルト文字列記述の生成に使われるString値プロパティ。組み込みObject.prototype.toString |
| %Symbol.unscopables% |
|
オブジェクト値プロパティで、自身と継承したプロパティ名が、関連オブジェクトのwith環境バインディングから除外されるプロパティ名となります。
|
6.1.6 数値型
ECMAScriptには2つの組み込み数値型、Number型とBigInt型があります。以下の
数値型は一般に精度損失や切り捨てなしには変換できないため、ECMAScript言語ではこれらの型間で暗黙的な変換を提供しません。型が異なる関数を呼び出す場合、プログラマはNumberやBigInt関数を使って明示的に変換する必要があります。
ECMAScriptの初版および後続版では、特定の演算子に対し、精度損失や
6.1.6.1 Number型
Number型は、18,437,736,874,454,810,627（すなわちNaNで生成されます。）一部の実装では外部コードにより異なるNaN値を検出できる場合もありますが、その挙動は
他にも+Infinity（または単にInfinity）、-Infinityで生成されます。）
その他18,437,736,874,454,810,624（
+0（または単に0）、-0で生成されます。）
18,437,736,874,454,810,622（
18,428,729,675,200,069,632（
ここでsは1または-1、mは
残りの9,007,199,254,740,990（
ここでsは1または-1、mは
大きさが253以下のすべての正負の
この仕様の「the Number value for
x」という表現（xは正確な実数数学量、πなどの無理数であってもよい）は、次の手順で選ばれたNumber値を意味します。Number型のすべての
一部のECMAScript演算子は、特定範囲の
6.1.6.1.1 Number::unaryMinus ( x )
抽象操作Number::unaryMinusは、引数x（Number型）を受け取り、Number型を返します。呼び出し時、次の手順を実行します：
- xが
NaN なら、NaN を返す。 - xの符号を反転したNumber値（絶対値は同じで符号が逆）を返す。
6.1.6.1.2 Number::bitwiseNOT ( x )
抽象操作Number::bitwiseNOTは、引数x（Number型）を受け取り、
6.1.6.1.3 Number::exponentiate ( base, exponent )
抽象操作Number::exponentiateは、引数base（Number型）とexponent（Number型）を受け取り、Number型を返します。baseのexponent乗の結果を表す
- exponentが
NaN ならNaN を返す。 - exponentが
+0 𝔽または-0 𝔽なら、1 𝔽を返す。 - baseが
NaN ならNaN を返す。 - baseが
+∞ 𝔽なら、- exponent >
+0 𝔽なら+∞ 𝔽を、そうでなければ+0 𝔽を返す。
- exponent >
- baseが
-∞ 𝔽なら、 - baseが
+0 𝔽なら、- exponent >
+0 𝔽なら+0 𝔽を、そうでなければ+∞ 𝔽を返す。
- exponent >
- baseが
-0 𝔽なら、 Assert : baseは有限 で、+0 𝔽でも-0 𝔽でもない。- exponentが
+∞ 𝔽なら、 - exponentが
-∞ 𝔽なら、 Assert : exponentは有限 で、+0 𝔽でも-0 𝔽でもない。- base <
-0 𝔽かつexponentが整数型Number でなければ、NaN を返す。 実装近似値 のNumber値（ℝ (base)のℝ (exponent)乗）を返す。
baseが** exponentの結果は、
6.1.6.1.4 Number::multiply ( x, y )
抽象操作Number::multiplyは、引数x（Number型）、y（Number型）を受け取り、Number型を返します。
6.1.6.1.5 Number::divide ( x, y )
抽象操作Number::divideは、引数x（Number型）、y（Number型）を受け取り、Number型を返します。
- xが
NaN またはyがNaN なら、NaN を返す。 - xが
+∞ 𝔽または-∞ 𝔽なら、- yが
+∞ 𝔽または-∞ 𝔽なら、NaN を返す。 - yが
+0 𝔽またはy >+0 𝔽ならxを返す。 - それ以外は-xを返す。
- yが
- yが
+∞ 𝔽なら、- xが
+0 𝔽またはx >+0 𝔽なら+0 𝔽を返す。そうでなければ-0 𝔽を返す。
- xが
- yが
-∞ 𝔽なら、- xが
+0 𝔽またはx >+0 𝔽なら-0 𝔽を返す。そうでなければ+0 𝔽を返す。
- xが
- xが
+0 𝔽または-0 𝔽なら、- yが
+0 𝔽または-0 𝔽なら、NaN を返す。 - y >
+0 𝔽ならxを返す。 - それ以外は-xを返す。
- yが
- yが
+0 𝔽なら、- x >
+0 𝔽なら+∞ 𝔽を返す。そうでなければ-∞ 𝔽を返す。
- x >
- yが
-0 𝔽なら、- x >
+0 𝔽なら-∞ 𝔽を返す。そうでなければ+∞ 𝔽を返す。
- x >
𝔽 (ℝ (x) /ℝ (y))を返す。
6.1.6.1.6 Number::remainder ( n, d )
抽象操作Number::remainderは、引数n（Number型）、d（Number型）を受け取り、Number型を返します。ここでnは被除数、dは除数であり、暗黙の除算から余りを返します。呼び出し時、次の手順を実行します：
CやC++では余り演算子は整数オペランドのみ受け付けますが、ECMAScriptでは浮動小数点オペランドも受け付けます。
%演算子で計算される）は、%の挙動を定義しています。これはCライブラリ関数fmodと比較できます。
6.1.6.1.7 Number::add ( x, y )
抽象操作Number::addは、引数x（Number型）、y（Number型）を受け取り、Number型を返します。
6.1.6.1.8 Number::subtract ( x, y )
抽象操作Number::subtractは、引数x（Number型）、y（Number型）を受け取り、Number型を返します。減算を行い、被減数xから減数yを引いた差を返します。呼び出し時、次の手順を実行します：
Number::add (x,Number::unaryMinus (y))を返す。
常にx - yはx + (-y)と同じ結果を生成します。
6.1.6.1.9 Number::leftShift ( x, y )
抽象操作Number::leftShiftは、引数x（Number型）、y（Number型）を受け取り、
6.1.6.1.10 Number::signedRightShift ( x, y )
抽象操作Number::signedRightShiftは、引数x（Number型）、y（Number型）を受け取り、
6.1.6.1.11 Number::unsignedRightShift ( x, y )
抽象操作Number::unsignedRightShiftは、引数x（Number型）、y（Number型）を受け取り、
6.1.6.1.12 Number::lessThan ( x, y )
抽象操作Number::lessThanは、引数x（Number型）、y（Number型）を受け取り、Booleanまたは
6.1.6.1.13 Number::equal ( x, y )
抽象操作Number::equalは、引数x（Number型）、y（Number型）を受け取り、Booleanを返します。呼び出し時、次の手順を実行します：
- xが
NaN ならfalse を返す。 - yが
NaN ならfalse を返す。 - xがyと等しければ
true を返す。 - xが
+0 𝔽かつyが-0 𝔽ならtrue を返す。 - xが
-0 𝔽かつyが+0 𝔽ならtrue を返す。 false を返す。
6.1.6.1.14 Number::sameValue ( x, y )
抽象操作Number::sameValueは、引数x（Number型）、y（Number型）を受け取り、Booleanを返します。呼び出し時、次の手順を実行します：
- xが
NaN かつyがNaN ならtrue を返す。 - xが
+0 𝔽かつyが-0 𝔽ならfalse を返す。 - xが
-0 𝔽かつyが+0 𝔽ならfalse を返す。 - xがyと等しければ
true を返す。 false を返す。
6.1.6.1.15 Number::sameValueZero ( x, y )
抽象操作Number::sameValueZeroは、引数x（Number型）、y（Number型）を受け取り、Booleanを返します。呼び出し時、次の手順を実行します：
- xが
NaN かつyがNaN ならtrue を返す。 - xが
+0 𝔽かつyが-0 𝔽ならtrue を返す。 - xが
-0 𝔽かつyが+0 𝔽ならtrue を返す。 - xがyと等しければ
true を返す。 false を返す。
6.1.6.1.16 NumberBitwiseOp ( op, x, y )
抽象操作NumberBitwiseOpは、引数op（&、^、|）、x（Number型）、y（Number型）を受け取り、
- lNumを!
ToInt32 (x)とする。 - rNumを!
ToInt32 (y)とする。 - lBitsを
ℝ (lNum)を表す32ビット2の補数ビット列とする。 - rBitsを
ℝ (rNum)を表す32ビット2の補数ビット列とする。 - opが
&なら、- resultをlBitsとrBitsにビットAND演算を適用した結果とする。
- そうでなくopが
^なら、- resultをlBitsとrBitsにビット排他的OR（XOR）演算を適用した結果とする。
- それ以外の場合、
Assert : opは|である。- resultをlBitsとrBitsにビットOR演算を適用した結果とする。
- resultで表される32ビット2の補数ビット列の
整数 に対応するNumber値 を返す。
6.1.6.1.17 Number::bitwiseAND ( x, y )
抽象操作Number::bitwiseANDは、引数x（Number型）、y（Number型）を受け取り、
NumberBitwiseOp (&, x, y)を返す。
6.1.6.1.18 Number::bitwiseXOR ( x, y )
抽象操作Number::bitwiseXORは、引数x（Number型）、y（Number型）を受け取り、
NumberBitwiseOp (^, x, y)を返す。
6.1.6.1.19 Number::bitwiseOR ( x, y )
抽象操作Number::bitwiseORは、引数x（Number型）、y（Number型）を受け取り、
NumberBitwiseOp (|, x, y)を返す。
6.1.6.1.20 Number::toString ( x, radix )
抽象操作Number::toStringは、引数x（Number型）、radix（
- xが
NaN なら"NaN" を返す。 - xが
+0 𝔽または-0 𝔽なら"0" を返す。 - x <
-0 𝔽なら、文字列連結 で"-" とNumber::toString (-x, radix)を連結して返す。 - xが
+∞ 𝔽なら"Infinity" を返す。 -
n、k、sを
整数 とし、k ≥ 1、radixk - 1 ≤ s < radixk、𝔽 (s × radixn - k)がxで、kが最小。kは基数radixで表現したsの桁数で、sはradixで割り切れず、最下位の桁は一意とは限らないことに注意。 - radix ≠ 10またはnが
-5から21の包含区間 なら、 - この場合、入力は科学的E表記（例：
1.2e+3）で表現される。 Assert : radixは10。- n < 0なら、
- exponentSignをコード単位0x002D（HYPHEN-MINUS）とする。
- それ以外、
- exponentSignをコード単位0x002B（PLUS SIGN）とする。
- k = 1なら、
- 最上位の10進桁のコード単位、コード単位0x002E（FULL STOP）、残りk -
1桁の10進表現のコード単位、コード単位0x0065（LATIN SMALL LETTER
E）、exponentSign、
abs (n - 1)の10進表現のコード単位を文字列連結 して返す。
ECMAScriptの実装者にはDavid M. Gayが書いた浮動小数点数の2進-10進変換の論文とコードが有用かもしれません：
Gay, David M. Correctly Rounded Binary-Decimal and Decimal-Binary Conversions.
Numerical Analysis, Manuscript 90-10. AT&T Bell Laboratories (Murray Hill,
New Jersey). 1990年11月30日。
https://ampl.com/_archive/first-website/REFS/rounding.pdf。
関連コードは
http://netlib.sandia.gov/fp/dtoa.c
および
http://netlib.sandia.gov/fp/g_fmt.c
にあり、他のnetlibミラーサイトにもあります。
6.1.6.2 BigInt型
BigInt型は、
6.1.6.2.1 BigInt::unaryMinus ( x )
抽象操作BigInt::unaryMinusは引数x（BigInt型）を受け取り、BigInt型を返します。呼び出し時、次の手順を実行します：
- x =
0 ℤなら0 ℤを返す。 - -xを返す。
6.1.6.2.2 BigInt::bitwiseNOT ( x )
抽象操作BigInt::bitwiseNOTは引数x（BigInt型）を受け取り、BigInt型を返します。xの1の補数を返します。呼び出し時、次の手順を実行します：
- -x -
1 ℤを返す。
6.1.6.2.3 BigInt::exponentiate ( base, exponent )
抽象操作BigInt::exponentiateは引数base（BigInt型）、exponent（BigInt型）を受け取り、
- exponent <
0 ℤならRangeError 例外を投げる。 - base =
0 ℤかつexponent =0 ℤなら1 ℤを返す。 - baseのexponent乗を返す。
6.1.6.2.4 BigInt::multiply ( x, y )
抽象操作BigInt::multiplyは引数x（BigInt型）、y（BigInt型）を受け取り、BigInt型を返します。呼び出し時、次の手順を実行します：
- x × yを返す。
6.1.6.2.5 BigInt::divide ( x, y )
抽象操作BigInt::divideは引数x（BigInt型）、y（BigInt型）を受け取り、
6.1.6.2.6 BigInt::remainder ( n, d )
抽象操作BigInt::remainderは引数n（BigInt型）、d（BigInt型）を受け取り、
6.1.6.2.7 BigInt::add ( x, y )
抽象操作BigInt::addは引数x（BigInt型）、y（BigInt型）を受け取り、BigInt型を返します。呼び出し時、次の手順を実行します：
- x + yを返す。
6.1.6.2.8 BigInt::subtract ( x, y )
抽象操作BigInt::subtractは引数x（BigInt型）、y（BigInt型）を受け取り、BigInt型を返します。呼び出し時、次の手順を実行します：
- x - yを返す。
6.1.6.2.9 BigInt::leftShift ( x, y )
抽象操作BigInt::leftShiftは引数x（BigInt型）、y（BigInt型）を受け取り、BigInt型を返します。呼び出し時、次の手順を実行します：
6.1.6.2.10 BigInt::signedRightShift ( x, y )
抽象操作BigInt::signedRightShiftは引数x（BigInt型）、y（BigInt型）を受け取り、BigInt型を返します。呼び出し時、次の手順を実行します：
BigInt::leftShift (x, -y)を返す。
6.1.6.2.11 BigInt::unsignedRightShift ( x, y )
抽象操作BigInt::unsignedRightShiftは引数x（BigInt型）、y（BigInt型）を受け取り、
TypeError 例外を投げる。
6.1.6.2.12 BigInt::lessThan ( x, y )
抽象操作BigInt::lessThanは引数x（BigInt型）、y（BigInt型）を受け取り、Boolean型を返します。呼び出し時、次の手順を実行します：
6.1.6.2.13 BigInt::equal ( x, y )
抽象操作BigInt::equalは引数x（BigInt型）、y（BigInt型）を受け取り、Boolean型を返します。呼び出し時、次の手順を実行します：
6.1.6.2.14 BinaryAnd ( x, y )
抽象操作BinaryAndは引数x（0または1）、y（0または1）を受け取り、0または1を返します。呼び出し時、次の手順を実行します：
- x = 1かつy = 1なら1を返す。
- それ以外は0を返す。
6.1.6.2.15 BinaryOr ( x, y )
抽象操作BinaryOrは引数x（0または1）、y（0または1）を受け取り、0または1を返します。呼び出し時、次の手順を実行します：
- x = 1またはy = 1なら1を返す。
- それ以外は0を返す。
6.1.6.2.16 BinaryXor ( x, y )
抽象操作BinaryXorは引数x（0または1）、y（0または1）を受け取り、0または1を返します。呼び出し時、次の手順を実行します：
- x = 1かつy = 0なら1を返す。
- それ以外でx = 0かつy = 1なら1を返す。
- それ以外は0を返す。
6.1.6.2.17 BigIntBitwiseOp ( op, x, y )
抽象操作BigIntBitwiseOpは、引数op（&、^、|）、x（BigInt型）、y（BigInt型）を受け取り、BigInt型を返します。呼び出し時、次の手順を実行します：
- xを
ℝ (x)に設定する。 - yを
ℝ (y)に設定する。 - resultを0に設定する。
- shiftを0に設定する。
- 次を満たすまで繰り返す：（x = 0またはx = -1）かつ（y = 0またはy = -1）
- opが
&なら、 - それ以外でopが
|なら、 - それ以外の場合、
- tmp ≠ 0なら、
- resultをresult - 2shiftに設定する。
- 注：これは符号拡張を行います。
- resultの
BigInt値 を返す。
6.1.6.2.18 BigInt::bitwiseAND ( x, y )
抽象操作BigInt::bitwiseANDは引数x（BigInt型）、y（BigInt型）を受け取り、BigInt型を返します。呼び出し時、次の手順を実行します：
BigIntBitwiseOp (&, x, y)を返す。
6.1.6.2.19 BigInt::bitwiseXOR ( x, y )
抽象操作BigInt::bitwiseXORは引数x（BigInt型）、y（BigInt型）を受け取り、BigInt型を返します。呼び出し時、次の手順を実行します：
BigIntBitwiseOp (^, x, y)を返す。
6.1.6.2.20 BigInt::bitwiseOR ( x, y )
抽象操作BigInt::bitwiseORは引数x（BigInt型）、y（BigInt型）を受け取り、BigInt型を返します。呼び出し時、次の手順を実行します：
BigIntBitwiseOp (|, x, y)を返す。
6.1.6.2.21 BigInt::toString ( x, radix )
抽象操作BigInt::toStringは引数x（BigInt型）、radix（
- x <
0 ℤなら、文字列連結 で"-" とBigInt::toString (-x, radix)を連結して返す。 - 基数radixで表現したxのString値を返す。
6.1.7 オブジェクト型
Object型の各インスタンス（単に「オブジェクト」とも呼ばれる）は、プロパティの集合を表します。各プロパティはデータプロパティまたはアクセサプロパティのいずれかです：
-
データプロパティは、キー値を
ECMAScript言語値 とBoolean属性の集合に関連付けます。 -
アクセサプロパティは、キー値を1つまたは2つのアクセサ関数とBoolean属性の集合に関連付けます。アクセサ関数は、そのプロパティに関連付けられた
ECMAScript言語値 の格納や取得に使われます。
オブジェクトのプロパティは
整数インデックスは、
すべてのオブジェクトは論理的にプロパティの集合ですが、プロパティのアクセスや操作の意味論が異なる複数の形式のオブジェクトが存在します。詳細は
さらに、一部のオブジェクトは呼び出し可能であり、これらは関数または
6.1.7.1 プロパティ属性
属性は、この仕様でObjectプロパティの状態を定義・説明するために使用されます（
| 属性名 | 属性が存在するプロパティの種類 | 値のドメイン | デフォルト値 | 説明 |
|---|---|---|---|---|
| [[Value]] |
|
|
|
getアクセスで取得されるプロパティの値。 |
| [[Writable]] |
|
Boolean |
|
|
| [[Get]] |
|
Object または |
|
値が |
| [[Set]] |
|
Object または |
|
値が |
| [[Enumerable]] |
|
Boolean |
|
|
| [[Configurable]] |
|
Boolean |
|
|
6.1.7.2 オブジェクトの内部メソッドと内部スロット
ECMAScriptにおけるオブジェクトの実際の意味論は、内部メソッドと呼ばれるアルゴリズムによって規定されます。ECMAScriptエンジンの各オブジェクトには、その実行時の挙動を定義する内部メソッドの集合が関連付けられています。これらの内部メソッドはECMAScript言語の一部ではありません。本仕様で説明目的のみで定義されます。ただし、ECMAScriptの各実装におけるオブジェクトは、その関連付けられた内部メソッドで規定されたとおりに動作しなければなりません。その実現方法の詳細は実装によって決まります。
内部メソッド名はポリモーフィックです。つまり、同じ内部メソッド名を呼び出しても、異なるオブジェクト値ごとに異なるアルゴリズムが実行される場合があります。内部メソッドが呼び出される実際のオブジェクトを「ターゲット」と呼びます。実行時に、あるアルゴリズムがオブジェクトのサポートしない内部メソッドを使おうとした場合、
内部スロットは、オブジェクトに関連付けられ、ECMAScript仕様のさまざまなアルゴリズムで使われる内部状態を表します。内部スロットはオブジェクトのプロパティではなく、継承もされません。各内部スロット仕様によっては、その状態はどの
すべてのオブジェクトには[[PrivateElements]]という名前の内部スロットがあり、これは
内部メソッドと内部スロットは、この仕様では[[ ]]で囲まれた名前で示されます。
通常のオブジェクトとは、次の条件をすべて満たすオブジェクトです：
-
表4 に挙げた内部メソッドについて、そのオブジェクトは10.1 で定義されたものを使う。 -
オブジェクトが[[Call]]内部メソッドを持つ場合、それは
10.2.1 または10.3.1 で定義されたもののいずれかを使う。 -
オブジェクトが[[Construct]]内部メソッドを持つ場合、それは
10.2.2 または10.3.2 で定義されたもののいずれかを使う。
エキゾチックオブジェクトとは、
本仕様では、
内部メソッドは、パラメータに加えて、常に呼び出し対象のオブジェクト自身にアクセスできます。
内部メソッドは暗黙的に
| 内部メソッド | シグネチャ | 説明 |
|---|---|---|
| [[GetPrototypeOf]] | ( ) → Object | Null |
このオブジェクトに継承プロパティを提供するオブジェクトを決定する。 |
| [[SetPrototypeOf]] | (Object | Null) → Boolean |
このオブジェクトに継承プロパティを提供する別のオブジェクトを関連付ける。 |
| [[IsExtensible]] | ( ) → Boolean | このオブジェクトに追加プロパティを追加できるかどうかを判定する。 |
| [[PreventExtensions]] | ( ) → Boolean |
このオブジェクトに新たなプロパティを追加できるかどうかを制御する。操作が成功したら |
| [[GetOwnProperty]] |
(propertyKey) → Undefined | |
このオブジェクトの所有プロパティでキーがpropertyKeyであるものについて、 |
| [[DefineOwnProperty]] | (propertyKey, PropertyDescriptor) → Boolean |
キーがpropertyKeyの所有プロパティをPropertyDescriptorで記述される状態に新規作成または変更する。プロパティの作成・更新に成功した場合は |
| [[HasProperty]] | (propertyKey) → Boolean | このオブジェクトが既に所有または継承するキーpropertyKeyのプロパティを持つかどうかを示すBoolean値を返す。 |
| [[Get]] | (propertyKey, Receiver) → any |
このオブジェクトからキーpropertyKeyのプロパティ値を返す。プロパティ値の取得にECMAScriptコードの実行が必要な場合、Receiverが |
| [[Set]] | (propertyKey, value, Receiver) → Boolean |
このオブジェクトのキーpropertyKeyのプロパティ値をvalueに設定する。値の設定にECMAScriptコードの実行が必要な場合、Receiverが |
| [[Delete]] | (propertyKey) → Boolean |
このオブジェクトからキーpropertyKeyの所有プロパティを削除する。削除できなかった場合（まだ存在する場合）は |
| [[OwnPropertyKeys]] |
( ) → |
オブジェクトのすべての所有 |
| 内部メソッド | シグネチャ | 説明 |
|---|---|---|
| [[Call]] |
(any, |
このオブジェクトに関連するコードを実行する。関数呼び出し式を介して呼び出される。内部メソッドの引数は |
| [[Construct]] |
( |
オブジェクトを生成する。new演算子またはsuper呼び出しで呼ばれる。内部メソッドの第1引数はsuper呼び出しの引数を要素とするnew演算子が最初に適用されたオブジェクト。これを実装するオブジェクトは |
6.1.7.3 本質的内部メソッドの不変条件
ECMAScriptエンジンのオブジェクトの内部メソッドは、以下に指定する不変条件を満たさなければなりません。本仕様の通常のECMAScriptオブジェクトおよびすべての標準
実装で提供される
実装は、必須内部メソッドの機能を不変条件を強制せずに別のインターフェースで提供するといった手段で、これらの不変条件を回避できるようにしてはなりません。
定義:
- 内部メソッドのターゲットとは、その内部メソッドが呼び出されるオブジェクトです。
-
ターゲットの[[IsExtensible]]内部メソッドが
false を返した、または[[PreventExtensions]]内部メソッドがtrue を返したことが観測された場合、ターゲットは拡張不可（non-extensible）です。 - 存在しない（non-existent）プロパティとは、拡張不可ターゲットの所有プロパティとして存在しないプロパティです。
-
SameValue へのすべての参照は、SameValue アルゴリズムの定義によります。
戻り値:
いかなる内部メソッドが返す値も、以下のいずれかの
- [[Type]] =
normal 、[[Target]] =empty 、[[Value]] = 下記に示すその内部メソッドの「通常の戻り値型」の値、または - [[Type]] =
throw 、[[Target]] =empty 、[[Value]] = 任意のECMAScript言語値 。
内部メソッドは
[[GetPrototypeOf]] ( )
- 通常の戻り値型はObjectまたはNullです。
-
ターゲットが拡張不可で[[GetPrototypeOf]]が値Vを返した場合、以後の[[GetPrototypeOf]]呼び出しも
SameValue としてVを返すべきです。
オブジェクトのプロトタイプチェーンは
[[SetPrototypeOf]] ( V )
- 通常の戻り値型はBooleanです。
-
ターゲットが拡張不可の場合、Vがターゲットの観測された[[GetPrototypeOf]]値と
SameValue でない限り、[[SetPrototypeOf]]はfalse を返さなければなりません。
[[IsExtensible]] ( )
- 通常の戻り値型はBooleanです。
-
[[IsExtensible]]が
false を返した場合、それ以降のターゲットへの[[IsExtensible]]呼び出しはすべてfalse を返さなければなりません。
[[PreventExtensions]] ( )
- 通常の戻り値型はBooleanです。
-
[[PreventExtensions]]が
true を返した場合、それ以降のターゲットへの[[IsExtensible]]呼び出しはすべてfalse を返し、ターゲットは拡張不可とみなされます。
[[GetOwnProperty]] ( P )
-
通常の戻り値型は
Property Descriptor またはUndefinedです。 -
戻り値が
Property Descriptor の場合、それは完全なProperty Descriptor でなければなりません。 -
Pが非設定可能かつ非書換可能な所有
データプロパティ である場合、以後の[[GetOwnProperty]](P)呼び出しは、[[Value]]がSameValue でPの[[Value]]属性と一致するProperty Descriptor を返さなければなりません。 -
Pの[[Writable]]・[[Value]]以外の属性が将来変更される、またはプロパティが削除される可能性がある場合、[[Configurable]]属性は
true でなければなりません。 -
[[Writable]]属性が
false からtrue に将来変更される可能性がある場合、[[Configurable]]属性はtrue でなければなりません。 -
ターゲットが拡張不可でPが存在しない場合、以後のターゲットへの[[GetOwnProperty]](P)呼び出しはPが存在しないものとして記述しなければなりません（つまり[[GetOwnProperty]](P)は
undefined を返さなければなりません）。
第3不変条件の帰結として、プロパティが
[[DefineOwnProperty]] ( P, Desc )
- 通常の戻り値型はBooleanです。
-
[[DefineOwnProperty]]は、Pが以前に非設定可能な所有プロパティとして観測されていた場合、次のいずれかを除き
false を返さなければなりません： -
[[DefineOwnProperty]](P,
Desc)は、ターゲットが拡張不可かつPが存在しない所有プロパティの場合
false を返さなければなりません。つまり、拡張不可なターゲットオブジェクトは新たなプロパティで拡張できません。
[[HasProperty]] ( P )
- 通常の戻り値型はBooleanです。
-
Pが以前にターゲットの非設定可能な所有データまたは
アクセサプロパティ として観測されていた場合、[[HasProperty]]はtrue を返さなければなりません。
[[Get]] ( P, Receiver )
-
通常の戻り値型は
ECMAScript言語型 です。 -
Pが以前にターゲットの非設定可能・非書換可能な所有
データプロパティ で値Vを持つと観測されていた場合、[[Get]]はVとSameValue な値を返さなければなりません。 -
Pが以前にターゲットの非設定可能な所有
アクセサプロパティ で、その[[Get]]属性がundefined だった場合、[[Get]]操作はundefined を返さなければなりません。
[[Set]] ( P, V, Receiver )
- 通常の戻り値型はBooleanです。
-
Pが以前にターゲットの非設定可能・非書換可能な所有
データプロパティ であった場合、[[Set]]はVがPの[[Value]]属性とSameValue でない限りfalse を返さなければなりません。 -
Pが以前にターゲットの非設定可能な所有
アクセサプロパティ で、その[[Set]]属性がundefined だった場合、[[Set]]操作はfalse を返さなければなりません。
[[Delete]] ( P )
- 通常の戻り値型はBooleanです。
-
Pが以前にターゲットの非設定可能な所有データまたは
アクセサプロパティ であった場合、[[Delete]]はfalse を返さなければなりません。
[[OwnPropertyKeys]] ( )
-
通常の戻り値型は
List です。 -
返される
List には重複要素があってはなりません。 -
返される
List の各要素は、プロパティキー でなければなりません。 -
返される
List には、これまでに観測されたすべての非設定可能な所有プロパティのキーが少なくとも含まれていなければなりません。 -
ターゲットが拡張不可の場合、返される
List には[[GetOwnProperty]]で観測可能なターゲットのすべての所有プロパティのキーのみが含まれていなければなりません。
[[Call]] ( )
-
通常の戻り値型は
ECMAScript言語型 です。
[[Construct]] ( )
- 通常の戻り値型はObjectです。
- ターゲットは[[Call]]内部メソッドも持っていなければなりません。
6.1.7.4 よく知られた組み込みオブジェクト
よく知られた組み込みオブジェクトは、この仕様書のアルゴリズムで明示的に参照される組み込みオブジェクトであり、通常は
この仕様書内では、%name% のような参照は、現在の
追加の項目は
6.2 ECMAScript 仕様タイプ
仕様タイプは、アルゴリズム内で ECMAScript 言語構成要素および
6.2.1 Enum 仕様タイプ
Enum は仕様内部でのみ使用され、ECMAScript コードから直接観測できない値です。Enum
は
6.2.2 List および Record 仕様タイプ
List 型は、new
式、関数呼び出し、その他のアルゴリズムで引数リスト（
アルゴリズムが List の要素を順序を明示せずに反復する場合、その順序は List の要素順です。
この仕様内では、リテラル構文で新しい List 値を表現できます。例えば、« 1, 2 » は 2 つの要素を持つ List 値を表し、それぞれ特定の値で初期化されます。新しい空の List は « » で表現できます。
この仕様書では、「A, B, ... の list-concatenation」という表現（各引数は空の場合もある List）で、各引数の要素を（順に）連結した新しい List 値を意味します。
List of Strings に対して、「辞書式コードユニット順でソートする」とは、短い方の文字列の長さまで各コードユニットの数値値でソートし、すべて等しい場合は短い文字列を先に並べることを意味します。これは抽象操作
Record 型は、この仕様のアルゴリズム内でデータの集約を記述するために使用されます。Record
型の値は 1 つ以上の名前付きフィールドからなります。各フィールドの値は
この仕様内ではオブジェクトリテラル風の構文で Record 値を表現できます。たとえば、{ [[Field1]]: 42, [[Field2]]:
仕様テキストやアルゴリズムでは、Record 値の特定のフィールドを参照するためにドット記法を使うことがあります。たとえば、前述の R というレコードに対して R.[[Field2]] は「R の [[Field2]] という名前のフィールド」を意味します。
よく使われる Record フィールドの組み合わせのスキーマには名前を付けることができ、その名前をリテラル Record
値の前に付与して、どの種類の集約が記述されているかを明示できます。例：PropertyDescriptor { [[Value]]: 42,
[[Writable]]:
6.2.3 Set および Relation 仕様タイプ
Set 型は、
Relation 型は、Set 上の制約を説明するために使われます。Relation 型の値は、その値領域の順序付きペアの Set です。たとえば、イベント上の Relation はイベントの順序付きペアの集合です。Relation R およびその値領域内の 2 つの値 a、b に対し、a R b は順序付きペア (a, b) が R の要素であることを略記しています。Relation は、ある条件に対してそれを満たす最小の Relation（最小 Relation）である場合、その条件に関する最小の Relation です。
狭義半順序(strict partial order) とは、Relation 値 R が次を満たすことです。
-
すべての a, b, c（R のドメイン内）について:
- a R a は成り立たない（反射性なし）
- a R b かつ b R c ならば a R c（推移性）
上記2つの性質は、それぞれ反射性なし(irreflexivity)・推移性(transitivity)と呼ばれます。
狭義全順序(strict total order) とは、Relation 値 R が次を満たすことです。
-
すべての a, b, c（R のドメイン内）について:
- a は b であるか、a R b か、b R a のいずれかである（全順序性）
- a R a は成り立たない（反射性なし）
- a R b かつ b R c ならば a R c（推移性）
上記3つの性質は、それぞれ全順序性(totality)・反射性なし(irreflexivity)・推移性(transitivity)と呼ばれます。
6.2.4 完了レコード仕様タイプ
Completion Record
仕様タイプは、値のランタイム伝播や、break、continue、return、throw
など、制御の非局所的な移動を行う文の動作など、制御フローを説明するために用いられます。
Completion Record には
| フィールド名 | 値 | 意味 |
|---|---|---|
| [[Type]] |
|
発生した完了の種類。 |
| [[Value]] |
|
生成された値。 |
| [[Target]] |
文字列または |
指定された制御移動のターゲットラベル。 |
Completion Record を指すために、以下のような略語が使われることがあります。
- normal completion は、[[Type]] の値が
normal である Completion Record を指します。 - break completion は、[[Type]] の値が
break である Completion Record を指します。 - continue completion は、[[Type]] の値が
continue である Completion Record を指します。 - return completion は、[[Type]] の値が
return である Completion Record を指します。 - throw completion は、[[Type]] の値が
throw である Completion Record を指します。 - abrupt completion は、[[Type]] の値が
normal 以外である Completion Record を指します。 - normal completion containing ある型の値を含む normal completion とは、その型の値が [[Value]] フィールドにある normal completion を指します。
この仕様で定義される呼び出し可能オブジェクトは、normal completion または throw completion のみを返します。それ以外の Completion Record を返すことは編集上の誤りとみなされます。
6.2.4.1 NormalCompletion ( value )
抽象操作 NormalCompletion は、引数 value（
Completion Record { [[Type]]:normal , [[Value]]: value, [[Target]]:empty } を返す。
6.2.4.2 ThrowCompletion ( value )
抽象操作 ThrowCompletion は、引数 value（
Completion Record { [[Type]]:throw , [[Value]]: value, [[Target]]:empty } を返す。
6.2.4.3 ReturnCompletion ( value )
抽象操作 ReturnCompletion は、引数 value（
Completion Record { [[Type]]:return , [[Value]]: value, [[Target]]:empty } を返す。
6.2.4.4 UpdateEmpty ( completionRecord, value )
抽象操作 UpdateEmpty は、引数 completionRecord（
アサート : completionRecord がreturn completion またはthrow completion のいずれかである場合、completionRecord.[[Value]] はempty であってはならない。- もし completionRecord.[[Value]] が
empty でなければ、? completionRecord を返す。 Completion Record { [[Type]]: completionRecord.[[Type]], [[Value]]: value, [[Target]]: completionRecord.[[Target]] } を返す。
6.2.5 参照レコード仕様タイプ
Reference Record
型は、delete、typeof、代入演算子、super
Reference Record は解決された名前または（まだ解決されていないかもしれない）プロパティバインディングであり、そのフィールドは
| フィールド名 | 値 | 意味 |
|---|---|---|
| [[Base]] | バインディングを保持している値または |
|
| [[ReferencedName]] | バインディングの名前。[[Base]] の値が |
|
| [[Strict]] | Boolean | |
| [[ThisValue]] | super |
この仕様で参照レコードを操作するために、以下の
6.2.5.1 IsPropertyReference ( V )
抽象操作 IsPropertyReference は、引数 V（
- もし V.[[Base]] が
unresolvable なら、false を返す。 - もし V.[[Base]] が
Environment Record ならfalse を返し、それ以外ならtrue を返す。
6.2.5.2 IsUnresolvableReference ( V )
抽象操作 IsUnresolvableReference は、引数 V（
- もし V.[[Base]] が
unresolvable ならtrue を返し、それ以外ならfalse を返す。
6.2.5.3 IsSuperReference ( V )
抽象操作 IsSuperReference は、引数 V（
- もし V.[[ThisValue]] が
empty でなければtrue を返し、それ以外ならfalse を返す。
6.2.5.4 IsPrivateReference ( V )
抽象操作 IsPrivateReference は、引数 V（
- もし V.[[ReferencedName]] が
Private Name であればtrue を返し、それ以外ならfalse を返す。
6.2.5.5 GetValue ( V )
抽象操作 GetValue は、引数 V（
- もし V が
Reference Record でなければ、V を返す。 IsUnresolvableReference (V) がtrue なら、ReferenceError 例外をスローする。IsPropertyReference (V) がtrue なら、- baseObj を ?
ToObject (V.[[Base]]) とする。 IsPrivateReference (V) がtrue なら、- ?
PrivateGet (baseObj, V.[[ReferencedName]]) を返す。
- ?
- V.[[ReferencedName]] が
property key でなければ、- V.[[ReferencedName]] を
?
ToPropertyKey (V.[[ReferencedName]]) とする。
- V.[[ReferencedName]] を
?
- ? baseObj.[[Get]](V.[[ReferencedName]],
GetThisValue (V)) を返す。
- baseObj を ?
- それ以外の場合、
- base を V.[[Base]] とする。
アサート : base はEnvironment Record である。- ? base.GetBindingValue(V.[[ReferencedName]], V.[[Strict]]) を返す（
9.1 参照）。
6.2.5.6 PutValue ( V, W )
抽象操作 PutValue は、引数 V（
- もし V が
Reference Record でなければ、ReferenceError 例外をスローする。 IsUnresolvableReference (V) がtrue なら、- もし V.[[Strict]] が
true なら、ReferenceError 例外をスローする。 - globalObj を
GetGlobalObject () とする。 - ?
Set (globalObj, V.[[ReferencedName]], W,false ) を実行する。 unused を返す。
- もし V.[[Strict]] が
IsPropertyReference (V) がtrue なら、- baseObj を ?
ToObject (V.[[Base]]) とする。 IsPrivateReference (V) がtrue なら、- ?
PrivateSet (baseObj, V.[[ReferencedName]], W) を返す。
- ?
- V.[[ReferencedName]] が
property key でなければ、- V.[[ReferencedName]] を
?
ToPropertyKey (V.[[ReferencedName]]) とする。
- V.[[ReferencedName]] を
?
- succeeded を ? baseObj.[[Set]](V.[[ReferencedName]], W,
GetThisValue (V)) とする。 - もし succeeded が
false かつ V.[[Strict]] がtrue なら、TypeError 例外をスローする。 unused を返す。
- baseObj を ?
- それ以外の場合、
- base を V.[[Base]] とする。
アサート : base はEnvironment Record である。- ? base.SetMutableBinding(V.[[ReferencedName]], W, V.[[Strict]]) を返す（
9.1 参照）。
6.2.5.7 GetThisValue ( V )
抽象操作 GetThisValue は、引数 V（
アサート :IsPropertyReference (V) がtrue であること。IsSuperReference (V) がtrue なら V.[[ThisValue]] を返し、そうでなければ V.[[Base]] を返す。
6.2.5.8 InitializeReferencedBinding ( V, W )
抽象操作 InitializeReferencedBinding は、引数 V（
アサート :IsUnresolvableReference (V) がfalse であること。- base を V.[[Base]] とする。
アサート : base はEnvironment Record であること。- ? base.InitializeBinding(V.[[ReferencedName]], W) を返す。
6.2.5.9 MakePrivateReference ( baseValue, privateIdentifier )
抽象操作 MakePrivateReference は、引数 baseValue（
- privateEnv を
実行中の実行コンテキスト の PrivateEnvironment とする。 アサート : privateEnv はnull であってはならない。- privateName を
ResolvePrivateIdentifier (privateEnv, privateIdentifier) とする。 - 次の
Reference Record を返す: { [[Base]]: baseValue, [[ReferencedName]]: privateName, [[Strict]]:true , [[ThisValue]]:empty }.
6.2.6 プロパティ記述子仕様タイプ
Property Descriptor
型は、オブジェクトプロパティ属性の操作および具現化を説明するために用いられます。Property Descriptor は、
Property Descriptor の値は、特定のフィールドの有無によってデータ Property Descriptor またはアクセサ Property Descriptor
に分類されることがあります。[[Value]] または [[Writable]]
という名前のフィールドが存在するものはデータ Property Descriptor です。[[Get]] または [[Set]] という名前のフィールドが存在するものはアクセサ Property Descriptor です。どの Property
Descriptor にも [[Enumerable]] および [[Configurable]] という名前のフィールドを持つことができます。Property Descriptor の値はデータ
Property Descriptor とアクセサ Property Descriptor の両方であってはなりませんが、どちらでもない場合もあります（この場合は汎用 Property
Descriptor です）。完全な Property Descriptor とは、アクセサ Property Descriptor
またはデータ Property Descriptor であり、かつ
この仕様で Property Descriptor の値を操作するために、以下の
6.2.6.1 IsAccessorDescriptor ( Desc )
抽象操作 IsAccessorDescriptor は、引数 Desc（
- もし Desc が [[Get]]
フィールドを持つなら、
true を返す。 - もし Desc が [[Set]]
フィールドを持つなら、
true を返す。 false を返す。
6.2.6.2 IsDataDescriptor ( Desc )
抽象操作 IsDataDescriptor は、引数 Desc（
- もし Desc が [[Value]]
フィールドを持つなら、
true を返す。 - もし Desc が [[Writable]]
フィールドを持つなら、
true を返す。 false を返す。
6.2.6.3 IsGenericDescriptor ( Desc )
抽象操作 IsGenericDescriptor は、引数 Desc（
IsAccessorDescriptor (Desc) がtrue なら、false を返す。IsDataDescriptor (Desc) がtrue なら、false を返す。true を返す。
6.2.6.4 FromPropertyDescriptor ( Desc )
抽象操作 FromPropertyDescriptor は、引数 Desc（
- もし Desc が
undefined なら、undefined を返す。 - obj を
OrdinaryObjectCreate (%Object.prototype% ) とする。 アサート : obj は自身のプロパティを持たない拡張可能なordinary object である。- もし Desc が [[Value]] フィールドを持つなら：
- !
CreateDataPropertyOrThrow (obj,"value" , Desc.[[Value]]) を実行する。
- !
- もし Desc が [[Writable]] フィールドを持つなら：
- !
CreateDataPropertyOrThrow (obj,"writable" , Desc.[[Writable]]) を実行する。
- !
- もし Desc が [[Get]] フィールドを持つなら：
- !
CreateDataPropertyOrThrow (obj,"get" , Desc.[[Get]]) を実行する。
- !
- もし Desc が [[Set]] フィールドを持つなら：
- !
CreateDataPropertyOrThrow (obj,"set" , Desc.[[Set]]) を実行する。
- !
- もし Desc が [[Enumerable]] フィールドを持つなら：
- !
CreateDataPropertyOrThrow (obj,"enumerable" , Desc.[[Enumerable]]) を実行する。
- !
- もし Desc が [[Configurable]] フィールドを持つなら：
- !
CreateDataPropertyOrThrow (obj,"configurable" , Desc.[[Configurable]]) を実行する。
- !
- obj を返す。
6.2.6.5 ToPropertyDescriptor ( Obj )
抽象操作 ToPropertyDescriptor は、引数 Obj（
- もし Obj が
オブジェクトでない なら、TypeError 例外をスローする。 - desc を新しい
Property Descriptor （初期状態でフィールドなし）とする。 - hasEnumerable を ?
HasProperty (Obj,"enumerable" ) とする。 - もし hasEnumerable が
true なら： - hasConfigurable を ?
HasProperty (Obj,"configurable" ) とする。 - もし hasConfigurable が
true なら： - hasValue を ?
HasProperty (Obj,"value" ) とする。 - もし hasValue が
true なら：- value を ?
Get (Obj,"value" ) とする。 - desc.[[Value]] に value を設定する。
- value を ?
- hasWritable を ?
HasProperty (Obj,"writable" ) とする。 - もし hasWritable が
true なら： - hasGet を ?
HasProperty (Obj,"get" ) とする。 - もし hasGet が
true なら：- getter を ?
Get (Obj,"get" ) とする。 IsCallable (getter) がfalse かつ getter がundefined でなければ、TypeError 例外をスローする。- desc.[[Get]] に getter を設定する。
- getter を ?
- hasSet を ?
HasProperty (Obj,"set" ) とする。 - もし hasSet が
true なら：- setter を ?
Get (Obj,"set" ) とする。 IsCallable (setter) がfalse かつ setter がundefined でなければ、TypeError 例外をスローする。- desc.[[Set]] に setter を設定する。
- setter を ?
- もし desc が [[Get]] フィールドまたは [[Set]] フィールドを持つなら：
- もし desc が [[Value]] フィールドまたは [[Writable]] フィールドを持つなら、
TypeError 例外をスローする。
- もし desc が [[Value]] フィールドまたは [[Writable]] フィールドを持つなら、
- desc を返す。
6.2.6.6 CompletePropertyDescriptor ( Desc )
抽象操作 CompletePropertyDescriptor は、引数 Desc（
- like を
Record { [[Value]]:undefined , [[Writable]]:false , [[Get]]:undefined , [[Set]]:undefined , [[Enumerable]]:false , [[Configurable]]:false } とする。 IsGenericDescriptor (Desc) がtrue またはIsDataDescriptor (Desc) がtrue なら、- もし Desc が [[Value]] フィールドを持たないなら、Desc.[[Value]] に like.[[Value]] を設定する。
- もし Desc が [[Writable]] フィールドを持たないなら、Desc.[[Writable]] に like.[[Writable]] を設定する。
- それ以外の場合：
- もし Desc が [[Get]] フィールドを持たないなら、Desc.[[Get]] に like.[[Get]] を設定する。
- もし Desc が [[Set]] フィールドを持たないなら、Desc.[[Set]] に like.[[Set]] を設定する。
- もし Desc が [[Enumerable]] フィールドを持たないなら、Desc.[[Enumerable]] に like.[[Enumerable]] を設定する。
- もし Desc が [[Configurable]] フィールドを持たないなら、Desc.[[Configurable]] に like.[[Configurable]] を設定する。
unused を返す。
6.2.7 環境レコード仕様タイプ
6.2.8 抽象クロージャ仕様タイプ
Abstract Closure
仕様タイプは、アルゴリズムのステップと値の集合をまとめて参照するために用いられます。Abstract Closure
はメタ値であり、closure(arg1, arg2) のような関数適用スタイルで呼び出されます。
Abstract Closure を生成するアルゴリズムステップでは、「capture」に続いてエイリアスのリストが記載され、その値がキャプチャされます。Abstract Closure が生成されると、それぞれのエイリアスに対応する値をその時点でキャプチャします。Abstract Closure を呼び出したときに実行されるアルゴリズムを指定するステップでは、各キャプチャされた値はキャプチャ時に使われたエイリアスで参照されます。
Abstract Closure が
Abstract Closure は他のアルゴリズムの一部としてインラインで作成され、次の例のように示されます。
- addend を 41 とする。
- closure を、パラメータ (x) を持ち addend
をキャプチャし、呼び出されたときに次のステップを実行する新しい
Abstract Closure とする：- x + addend を返す。
- val を closure(1) とする。
アサート : val は 42 である。
6.2.9 データブロック
Data Block
仕様タイプは、個別かつ可変なバイト（8ビット）値のシーケンスを記述するために用いられます。byte
value とは、
この仕様内では、記法上の便宜のため、Data Block 値の個々のバイトにアクセスするために配列風の構文を使うことができます。この記法は、Data Block 値を 0
基点の
複数の
Shared Data Block のセマンティクスは、
この仕様で Data Block 値を操作するために、以下の
6.2.9.1 CreateByteDataBlock ( size )
抽象操作 CreateByteDataBlock は、引数 size（非負の
- もし size > 253 - 1 なら、
RangeError 例外をスローする。 - db を size バイトからなる新しい
Data Block 値とする。そのようなData Block を生成できない場合、RangeError 例外をスローする。 - db のすべてのバイトを 0 に設定する。
- db を返す。
6.2.9.2 CreateSharedByteDataBlock ( size )
抽象操作 CreateSharedByteDataBlock は、引数 size（非負の
- db を size バイトからなる新しい
Shared Data Block 値とする。そのようなShared Data Block を生成できない場合、RangeError 例外をスローする。 - execution を
周囲のエージェント のAgent Record の [[CandidateExecution]] フィールドとする。 - eventsRecord を execution.[[EventsRecords]] のうち、[[AgentSignifier]] が
AgentSignifier () であるAgent Events Record とする。 - zero を « 0 » とする。
- db の各インデックス i について、
WriteSharedMemory { [[Order]]:init , [[NoTear]]:true , [[Block]]: db, [[ByteIndex]]: i, [[ElementSize]]: 1, [[Payload]]: zero } を eventsRecord.[[EventList]] に追加する。
- db を返す。
6.2.9.3 CopyDataBlockBytes ( toBlock, toIndex, fromBlock, fromIndex, count )
抽象操作 CopyDataBlockBytes は、引数 toBlock（
アサート : fromBlock と toBlock は異なる値であること。- fromSize を fromBlock のバイト数とする。
アサート : fromIndex + count ≤ fromSize であること。- toSize を toBlock のバイト数とする。
アサート : toIndex + count ≤ toSize であること。- count > 0 の間、繰り返す：
- もし fromBlock が
Shared Data Block なら、- execution を
周囲のエージェント のAgent Record の [[CandidateExecution]] フィールドとする。 - eventsRecord を execution.[[EventsRecords]] のうち、[[AgentSignifier]] が
AgentSignifier () であるAgent Events Record とする。 - bytes を、唯一の要素が非決定的に選択された
byte value であるList とする。 - 注：実装において bytes は基盤ハードウェア上の非アトミックな読み取り命令の結果です。非決定性は
メモリーモデル の意味的要請であり、弱い一貫性を持つハードウェアの観測可能な挙動を記述するためのものです。 - readEvent を
ReadSharedMemory { [[Order]]:unordered , [[NoTear]]:true , [[Block]]: fromBlock, [[ByteIndex]]: fromIndex, [[ElementSize]]: 1 } とする。 - readEvent を eventsRecord.[[EventList]] に追加する。
Chosen Value Record { [[Event]]: readEvent, [[ChosenValue]]: bytes } を execution.[[ChosenValues]] に追加する。- もし toBlock が
Shared Data Block なら、WriteSharedMemory { [[Order]]:unordered , [[NoTear]]:true , [[Block]]: toBlock, [[ByteIndex]]: toIndex, [[ElementSize]]: 1, [[Payload]]: bytes } を eventsRecord.[[EventList]] に追加する。
- それ以外の場合：
- toBlock[toIndex] に bytes[0] を設定する。
- execution を
- それ以外の場合：
アサート : toBlock はShared Data Block でないこと。- toBlock[toIndex] に fromBlock[fromIndex] を設定する。
- toIndex を toIndex + 1 に設定する。
- fromIndex を fromIndex + 1 に設定する。
- count を count - 1 に設定する。
- もし fromBlock が
unused を返す。
6.2.10 PrivateElement 仕様タイプ
PrivateElement 型は、プライベートクラスフィールド・メソッド・アクセサの仕様で使用される
PrivateElement 型の値は、
| フィールド名 | そのフィールドが存在する [[Kind]] フィールドの値 | 値 | 意味 |
|---|---|---|---|
| [[Key]] | 全て |
|
フィールド、メソッド、またはアクセサの名前。 |
| [[Kind]] | 全て |
|
要素の種類。 |
| [[Value]] |
|
|
フィールドの値。 |
| [[Get]] |
|
|
プライベートアクセサの getter。 |
| [[Set]] |
|
|
プライベートアクセサの setter。 |
6.2.11 ClassFieldDefinition レコード仕様タイプ
ClassFieldDefinition 型は、クラスフィールドの仕様で使用される
ClassFieldDefinition 型の値は
| フィールド名 | 値 | 意味 |
|---|---|---|
| [[Name]] |
|
フィールドの名前。 |
| [[Initializer]] |
ECMAScript |
フィールドの初期化子（あれば）。 |
6.2.12 プライベート名
Private Name
仕様タイプは、プライベートクラス要素（フィールド、メソッド、アクセサ）のキーを表すグローバルに一意な値（たとえ他の Private Name
と区別がつかなくても、必ず異なる値）を記述するために用いられます。各 Private Name には、
6.2.13 ClassStaticBlockDefinition レコード仕様タイプ
ClassStaticBlockDefinition
Record は、クラスの static 初期化ブロックの実行可能なコードをカプセル化するために用いられる
ClassStaticBlockDefinition Record は、
| フィールド名 | 値 | 意味 |
|---|---|---|
| [[BodyFunction]] |
ECMAScript |
クラスの static 初期化時に呼び出される |
7 抽象操作
これらの操作は ECMAScript 言語の一部ではなく、ECMAScript 言語のセマンティクス仕様を補助するためだけにここで定義されています。他にも、より専門的な
7.1 型変換
ECMAScript 言語は必要に応じて暗黙的に自動型変換を行います。特定の構文のセマンティクスを明確にするために、一連の変換
7.1.1 ToPrimitive ( input [ , preferredType ] )
抽象操作 ToPrimitive は、引数 input（
- もし input が
オブジェクト なら、- exoticToPrim を ?
GetMethod (input,%Symbol.toPrimitive% ) とする。 - もし exoticToPrim が
undefined でなければ、- もし preferredType が与えられていなければ、
- hint を
"default" とする。
- hint を
- そうでなく、preferredType が
string なら、- hint を
"string" とする。
- hint を
- それ以外の場合、
アサート : preferredType はnumber である。- hint を
"number" とする。
- result を ?
Call (exoticToPrim, input, « hint » ) とする。 - もし result が
オブジェクトでなければ result を返す。 TypeError 例外をスローする。
- もし preferredType が与えられていなければ、
- もし preferredType が与えられていなければ、preferredType を
number とする。 - ?
OrdinaryToPrimitive (input, preferredType) を返す。
- exoticToPrim を ?
- input を返す。
ToPrimitive がヒントなしで呼ばれた場合、一般的にはヒントが
7.1.1.1 OrdinaryToPrimitive ( O, hint )
抽象操作 OrdinaryToPrimitive は、引数 O（オブジェクト）と
hint（
- もし hint が
string なら、- methodNames を «
"toString" ,"valueOf" » とする。
- methodNames を «
- それ以外の場合、
- methodNames を «
"valueOf" ,"toString" » とする。
- methodNames を «
- methodNames の各要素 name について、
- method を ?
Get (O, name) とする。 - もし
IsCallable (method) がtrue なら、- result を ?
Call (method, O) とする。 - もし result が
オブジェクトでなければ result を返す。
- result を ?
- method を ?
TypeError 例外をスローする。
7.1.2 ToBoolean ( argument )
抽象操作 ToBoolean は、引数 argument（
7.1.3 ToNumeric ( value )
抽象操作 ToNumeric は、引数 value（
- primValue を ?
ToPrimitive (value,number ) とする。 - もし primValue が
BigInt なら、primValue を返す。 - ?
ToNumber (primValue) を返す。
7.1.4 ToNumber ( argument )
抽象操作 ToNumber は、引数 argument（
- もし argument が
Number なら、argument を返す。 - もし argument が Symbol または BigInt なら、
TypeError 例外をスローする。 - もし argument が
undefined なら、NaN を返す。 - もし argument が
null またはfalse なら、+0 𝔽 を返す。 - もし argument が
true なら、1 𝔽 を返す。 - もし argument が
文字列 なら、StringToNumber (argument) を返す。 アサート : argument はオブジェクト である。- primValue を ?
ToPrimitive (argument,number ) とする。 アサート : primValue はオブジェクトでない こと。- ?
ToNumber (primValue) を返す。
7.1.4.1 文字列型に適用される ToNumber
抽象操作
構文
上記で明示的に定義されていない全ての文法記号は、数値リテラルの字句文法（
-
StringNumericLiteral には、先頭および/または末尾に空白や行終端記号を含めることができます。 -
10進数である
StringNumericLiteral には、任意個数の先頭0桁が含まれてよいです。 -
10進数である
StringNumericLiteral には、符号を示すために+や-を含めることができます。 -
空もしくは空白のみの
StringNumericLiteral は+0 𝔽 に変換されます。 -
Infinityおよび-InfinityはStringNumericLiteral では認識されますが、NumericLiteral では認識されません。 -
StringNumericLiteral にはBigIntLiteralSuffix を含めることはできません。 -
StringNumericLiteral にはNumericLiteralSeparator を含めることはできません。
7.1.4.1.1 StringToNumber ( str )
抽象操作 StringToNumber は、引数 str（文字列）を受け取り、数値を返します。呼び出されたとき、次の手順を実行します：
- literal を
ParseText (str,StringNumericLiteral ) とする。 - もし literal が
List のエラーであれば、NaN を返す。 - literal の
StringNumericValue を返す。
7.1.4.1.2 実行時セマンティクス: StringNumericValue
以下の生成規則に対し分割的に定義されます：
+0 𝔽 を返す。
NonDecimalIntegerLiteral の MV を𝔽 で返す。
- a を
StrUnsignedDecimalLiteral のStringNumericValue とする。 - もし a が
+0 𝔽 なら-0 𝔽 を返す。 - -a を返す。
+∞ 𝔽 を返す。
- 最初の
DecimalDigits の MV を a とする。 - 2番目の
DecimalDigits が存在する場合、- 2番目の
DecimalDigits の MV を b とする。 - 2番目の
DecimalDigits の符号位置数を n とする。
- 2番目の
- それ以外の場合、
- b を 0 とする。
- n を 0 とする。
ExponentPart が存在する場合、e をExponentPart の MV とし、それ以外の場合 e を 0 とする。RoundMVResult ((a + (b × 10-n)) × 10e) を返す。
DecimalDigits の MV を b とする。ExponentPart が存在する場合、e をExponentPart の MV とし、それ以外の場合 e を 0 とする。DecimalDigits の符号位置数を n とする。RoundMVResult (b × 10e - n) を返す。
DecimalDigits の MV を a とする。ExponentPart が存在する場合、e をExponentPart の MV とし、それ以外の場合 e を 0 とする。RoundMVResult (a × 10e) を返す。
7.1.4.1.3 RoundMVResult ( n )
抽象操作 RoundMVResult は、引数 n（
7.1.5 ToIntegerOrInfinity ( argument )
抽象操作 ToIntegerOrInfinity は、引数 argument（
7.1.6 ToInt32 ( argument )
抽象操作 ToInt32 は、引数 argument（
上記 ToInt32 の定義により：
- ToInt32 抽象操作は冪等性を持ちます：その結果に再度適用しても値は変わりません。
-
ToInt32(
ToUint32 (x)) は、任意の x に対し ToInt32(x) と同じ値を返します。（この性質を保つために、+∞ 𝔽 と-∞ 𝔽 は+0 𝔽 に変換されます。） -
ToInt32 は
-0 𝔽 を+0 𝔽 にマッピングします。
7.1.7 ToUint32 ( argument )
抽象操作 ToUint32 は、引数 argument（
7.1.8 ToInt16 ( argument )
抽象操作 ToInt16 は、引数 argument（
7.1.9 ToUint16 ( argument )
抽象操作 ToUint16 は、引数 argument（
7.1.10 ToInt8 ( argument )
抽象操作 ToInt8 は、引数 argument（
7.1.11 ToUint8 ( argument )
抽象操作 ToUint8 は、引数 argument（
7.1.12 ToUint8Clamp ( argument )
抽象操作 ToUint8Clamp は、引数 argument（
他のほとんどの ECMAScript Math.round
7.1.13 ToBigInt ( argument )
抽象操作 ToBigInt は、引数 argument（
- prim を ?
ToPrimitive (argument,number ) とする。 - prim に対応する値を
表12 から返す。
| 引数の型 | 結果 |
|---|---|
| Undefined |
|
| Null |
|
| Boolean |
prim が 1n、prim
が 0n を返す。
|
| BigInt | prim を返す。 |
| Number |
|
| String |
|
| Symbol |
|
7.1.14 StringToBigInt ( str )
抽象操作 StringToBigInt は、引数 str（文字列）を受け取り、BigInt または
7.1.14.1 StringIntegerLiteral 文法
構文
7.1.14.2 実行時セマンティクス: MV
-
StringIntegerLiteral ::: StrWhiteSpace opt -
StringIntegerLiteral ::: StrWhiteSpace opt StrIntegerLiteral StrWhiteSpace opt StrIntegerLiteral の MV です。
7.1.15 ToBigInt64 ( argument )
抽象操作 ToBigInt64 は、引数 argument（
7.1.16 ToBigUint64 ( argument )
抽象操作 ToBigUint64 は、引数 argument（
7.1.17 ToString ( argument )
抽象操作 ToString は、引数 argument（
- もし argument が
文字列 なら、argument を返す。 - もし argument が
シンボル なら、TypeError 例外を投げる。 - もし argument が
undefined なら、"undefined" を返す。 - もし argument が
null なら、"null" を返す。 - もし argument が
true なら、"true" を返す。 - もし argument が
false なら、"false" を返す。 - もし argument が
数値 なら、Number::toString (argument, 10) を返す。 - もし argument が
BigInt なら、BigInt::toString (argument, 10) を返す。 アサート : argument はオブジェクト である。- primValue を ?
ToPrimitive (argument,string ) とする。 アサート : primValue はオブジェクトでない こと。- ?
ToString (primValue) を返す。
7.1.18 ToObject ( argument )
抽象操作 ToObject は、引数 argument（
| 引数の型 | 結果 |
|---|---|
| Undefined |
|
| Null |
|
| Boolean |
[[BooleanData]] 内部スロットが argument
に設定された新しい Boolean オブジェクトを返す。Boolean オブジェクトの説明は |
| Number |
[[NumberData]] 内部スロットが argument
に設定された新しい Number オブジェクトを返す。Number オブジェクトの説明は |
| String |
[[StringData]] 内部スロットが argument
に設定された新しい String オブジェクトを返す。String オブジェクトの説明は |
| Symbol |
[[SymbolData]] 内部スロットが argument
に設定された新しい Symbol オブジェクトを返す。Symbol オブジェクトの説明は |
| BigInt |
[[BigIntData]] 内部スロットが argument
に設定された新しい BigInt オブジェクトを返す。BigInt オブジェクトの説明は |
| Object | argument を返す。 |
7.1.19 ToPropertyKey ( argument )
抽象操作 ToPropertyKey は、引数 argument（
- key を ?
ToPrimitive (argument,string ) とする。 - もし key が
シンボル なら、- key を返す。
- !
ToString (key) を返す。
7.1.20 ToLength ( argument )
抽象操作 ToLength は、引数 argument（
- len を ?
ToIntegerOrInfinity (argument) とする。 - もし len ≤ 0 なら、
+0 𝔽 を返す。 𝔽 (min (len, 253 - 1)) を返す。
7.1.21 CanonicalNumericIndexString ( argument )
抽象操作 CanonicalNumericIndexString は、引数 argument（文字列）を受け取り、数値または
canonical numeric string
とは、CanonicalNumericIndexString 抽象操作が
7.1.22 ToIndex ( value )
抽象操作 ToIndex は、引数 value（
- integer を ?
ToIntegerOrInfinity (value) とする。 - もし integer が
区間 0 から 253 - 1 に含まれていなければ、RangeError 例外を投げる。 - integer を返す。
7.2 テストおよび比較操作
7.2.1 RequireObjectCoercible ( argument )
抽象操作 RequireObjectCoercible は、引数 argument（
| 引数の型 | 結果 |
|---|---|
| Undefined |
|
| Null |
|
| Boolean | argument を返す。 |
| Number | argument を返す。 |
| String | argument を返す。 |
| Symbol | argument を返す。 |
| BigInt | argument を返す。 |
| Object | argument を返す。 |
7.2.2 IsArray ( argument )
抽象操作 IsArray は、引数 argument（
- もし argument が
オブジェクトでない 場合、false を返す。 - もし argument が
配列エキゾチックオブジェクト ならtrue を返す。 - もし argument が
Proxy エキゾチックオブジェクト なら、- ?
ValidateNonRevokedProxy (argument) を行う。 - proxyTarget を argument.[[ProxyTarget]] とする。
- ?
IsArray (proxyTarget) を返す。
- ?
false を返す。
7.2.3 IsCallable ( argument )
抽象操作 IsCallable は、引数 argument（
- もし argument が
オブジェクトでない 場合、false を返す。 - もし argument が [[Call]] 内部メソッドを持てば
true を返す。 false を返す。
7.2.4 IsConstructor ( argument )
抽象操作 IsConstructor は、引数 argument（
- もし argument が
オブジェクトでない 場合、false を返す。 - もし argument が [[Construct]] 内部メソッドを持てば
true を返す。 false を返す。
7.2.5 IsExtensible ( O )
抽象操作 IsExtensible は、引数 O（オブジェクト）を受け取り、
- ? O.[[IsExtensible]]() を返す。
7.2.6 IsRegExp ( argument )
抽象操作 IsRegExp は、引数 argument（
- もし argument が
オブジェクトでない 場合、false を返す。 - matcher を ?
Get (argument,%Symbol.match% ) とする。 - もし matcher が
undefined でなければ、ToBoolean (matcher) を返す。 - もし argument が [[RegExpMatcher]]
内部スロットを持てば、
true を返す。 false を返す。
7.2.7 静的セマンティクス: IsStringWellFormedUnicode ( string )
抽象操作 IsStringWellFormedUnicode は、引数 string（文字列）を受け取り、Boolean を返します。string を
- len を string の長さとする。
- k を 0 とする。
- 繰り返し、k < len の間:
- cp を
CodePointAt (string, k) とする。 - もし cp.[[IsUnpairedSurrogate]] が
true なら、false を返す。 - k を k + cp.[[CodeUnitCount]] に設定する。
- cp を
true を返す。
7.2.8 SameType ( x, y )
抽象操作 SameType は、引数 x（
- もし x が
undefined かつ y もundefined ならtrue を返す。 - もし x が
null かつ y もnull ならtrue を返す。 - もし x が
Boolean かつ y もBoolean ならtrue を返す。 - もし x が
Number かつ y もNumber ならtrue を返す。 - もし x が
BigInt かつ y もBigInt ならtrue を返す。 - もし x が
シンボル かつ y もシンボル ならtrue を返す。 - もし x が
文字列 かつ y も文字列 ならtrue を返す。 - もし x が
オブジェクト かつ y もオブジェクト ならtrue を返す。 false を返す。
7.2.9 SameValue ( x, y )
抽象操作 SameValue は、引数 x（
- もし
SameType (x, y) がfalse なら、false を返す。 - もし x が
Number なら、Number::sameValue (x, y) を返す。
SameValueNonNumber (x, y) を返す。
このアルゴリズムは
7.2.10 SameValueZero ( x, y )
抽象操作 SameValueZero は、引数 x（
- もし
SameType (x, y) がfalse なら、false を返す。 - もし x が
Number なら、Number::sameValueZero (x, y) を返す。
SameValueNonNumber (x, y) を返す。
SameValueZero は
7.2.11 SameValueNonNumber ( x, y )
抽象操作 SameValueNonNumber は、引数 x（
アサート :SameType (x, y) はtrue である。- もし x が
undefined またはnull なら、true を返す。 - もし x が
BigInt なら、BigInt::equal (x, y) を返す。
- もし x が
文字列 なら、- もし x と y の長さが等しく、かつ同じ位置のコード単位が全て一致するなら
true を返し、そうでなければfalse を返す。
- もし x と y の長さが等しく、かつ同じ位置のコード単位が全て一致するなら
- もし x が
Boolean なら、- もし x と y がともに
true かともにfalse ならtrue を返し、そうでなければfalse を返す。
- もし x と y がともに
- 注：その他の
ECMAScript 言語値 は同一性(identity)で比較されます。 - もし x が y であれば
true 、そうでなければfalse を返す。
7.2.12 IsLessThan ( x, y, LeftFirst )
抽象操作 IsLessThan は、引数 x（
- もし LeftFirst が
true なら、- px を ?
ToPrimitive (x,number ) とする。 - py を ?
ToPrimitive (y,number ) とする。
- px を ?
- それ以外の場合、
- 注：評価順を逆にすることで左から右の評価を保証する必要がある。
- py を ?
ToPrimitive (y,number ) とする。 - px を ?
ToPrimitive (x,number ) とする。
- もし px が
文字列 かつ py も文字列 なら、 - それ以外の場合、
- もし px が
BigInt かつ py が文字列 なら、- ny を
StringToBigInt (py) とする。 - もし ny が
undefined ならundefined を返す。 BigInt::lessThan (px, ny) を返す。
- ny を
- もし px が
文字列 かつ py がBigInt なら、- nx を
StringToBigInt (px) とする。 - もし nx が
undefined ならundefined を返す。 BigInt::lessThan (nx, py) を返す。
- nx を
- 注：px と py はプリミティブ値なので評価順は重要でない。
- nx を ?
ToNumeric (px) とする。 - ny を ?
ToNumeric (py) とする。 - もし
SameType (nx, ny) がtrue なら、- もし nx が
Number なら、Number::lessThan (nx, ny) を返す。
- それ以外の場合、
アサート : nx はBigInt である。BigInt::lessThan (nx, ny) を返す。
- もし nx が
アサート : nx はBigInt で、ny はNumber 、または nx はNumber で ny はBigInt 。- もし nx または ny が
NaN ならundefined を返す。 - もし nx が
-∞ 𝔽 または ny が+∞ 𝔽 ならtrue を返す。 - もし nx が
+∞ 𝔽 または ny が-∞ 𝔽 ならfalse を返す。 - もし
ℝ (nx) <ℝ (ny) ならtrue を返し、そうでなければfalse を返す。
- もし px が
文字列の比較は UTF-16 コード単位列に対する単純な辞書順比較を用います。Unicode
仕様で定義されるより複雑で意味論的な文字・文字列の等価性や照合順序は考慮されません。そのため、Unicode
標準で正規等価な値であっても正規化形式が異なる場合は等価判定されないことがあります。また、コード単位による辞書順は、
7.2.13 IsLooselyEqual ( x, y )
抽象操作 IsLooselyEqual は、引数 x（== 演算子の意味を与えます。呼び出されたとき、次の手順を実行します：
- もし
SameType (x, y) がtrue なら、IsStrictlyEqual (x, y) を返す。
- もし x が
null かつ y がundefined ならtrue を返す。 - もし x が
undefined かつ y がnull ならtrue を返す。 - 注：このステップは
B.3.6.2 で置き換えられます。 - もし x が
Number かつ y が文字列 なら、!IsLooselyEqual (x, !ToNumber (y)) を返す。 - もし x が
文字列 かつ y がNumber なら、!IsLooselyEqual (!ToNumber (x), y) を返す。 - もし x が
BigInt かつ y が文字列 なら、- n を
StringToBigInt (y) とする。 - もし n が
undefined ならfalse を返す。 - !
IsLooselyEqual (x, n) を返す。
- n を
- もし x が
文字列 かつ y がBigInt なら、!IsLooselyEqual (y, x) を返す。 - もし x が
Boolean なら、!IsLooselyEqual (!ToNumber (x), y) を返す。 - もし y が
Boolean なら、!IsLooselyEqual (x, !ToNumber (y)) を返す。 - もし x が 文字列、数値、BigInt、またはシンボルのいずれかで y が
オブジェクト なら、!IsLooselyEqual (x, ?ToPrimitive (y)) を返す。 - もし x が
オブジェクト かつ y が 文字列、数値、BigInt、またはシンボルのいずれかなら、!IsLooselyEqual (?ToPrimitive (x), y) を返す。 - もし x が
BigInt かつ y がNumber 、または x がNumber かつ y がBigInt なら、 false を返す。
7.2.14 IsStrictlyEqual ( x, y )
抽象操作 IsStrictlyEqual は、引数 x（=== 演算子の意味を与えます。呼び出されたとき、次の手順を実行します：
- もし
SameType (x, y) がfalse なら、false を返す。 - もし x が
Number なら、Number::equal (x, y) を返す。
SameValueNonNumber (x, y) を返す。
このアルゴリズムは
7.3 オブジェクトに対する操作
7.3.1 MakeBasicObject ( internalSlotsList )
抽象操作 MakeBasicObject は、引数 internalSlotsList（
- internalSlotsList を
リスト連結 で internalSlotsList と « [[PrivateElements]] » の連結に設定する。 - internalSlotsList の各名前に対応する内部スロットを持つ新しいオブジェクト obj を生成する。
- 注：
オブジェクトの内部メソッドと内部スロット で説明されているように、これらの内部スロットの初期値は特に指定がない限りundefined である。 - obj.[[PrivateElements]] を新しい空の
リスト に設定する。 - obj の本質的な内部メソッドを、
通常オブジェクト の10.1 で規定されるデフォルトの定義に設定する。 アサート : 呼び出し元が obj の [[GetPrototypeOf]] および [[SetPrototypeOf]] の両方の本質的な内部メソッドを上書きしないなら、internalSlotsList は [[Prototype]] を含む。アサート : 呼び出し元が obj の [[SetPrototypeOf]], [[IsExtensible]], [[PreventExtensions]] の全ての本質的な内部メソッドを上書きしないなら、internalSlotsList は [[Extensible]] を含む。- もし internalSlotsList が [[Extensible]]
を含むなら、obj.[[Extensible]] を
true に設定する。 - obj を返す。
本仕様内では、
7.3.2 Get ( O, P )
抽象操作 Get は、引数 O（オブジェクト）と P（
- ? O.[[Get]](P, O) を返す。
7.3.3 GetV ( V, P )
抽象操作 GetV は、引数 V（
- O を ?
ToObject (V) とする。 - ? O.[[Get]](P, V) を返す。
7.3.4 Set ( O, P, V, Throw )
抽象操作 Set は、引数 O（オブジェクト）、P（
- success を ? O.[[Set]](P, V, O) とする。
- もし success が
false かつ Throw がtrue なら、TypeError 例外を投げる。 unused を返す。
7.3.5 CreateDataProperty ( O, P, V )
抽象操作 CreateDataProperty は、引数 O（オブジェクト）、P（
- newDesc を PropertyDescriptor { [[Value]]:
V, [[Writable]]:
true , [[Enumerable]]:true , [[Configurable]]:true } とする。 - ? O.[[DefineOwnProperty]](P, newDesc) を返す。
この抽象操作は、ECMAScript
言語の代入演算子によって作成されるプロパティと同じデフォルト属性でプロパティを生成します。通常、このプロパティは既存しません。もし既に存在し、それが設定可能でない場合や
O が拡張不可能な場合、[[DefineOwnProperty]] は
7.3.6 CreateDataPropertyOrThrow ( O, P, V )
抽象操作 CreateDataPropertyOrThrow は、引数 O（オブジェクト）、P（
- success を ?
CreateDataProperty (O, P, V) とする。 - もし success が
false なら、TypeError 例外を投げる。 unused を返す。
この抽象操作は、ECMAScript
言語の代入演算子によって作成されるプロパティと同じデフォルト属性でプロパティを生成します。通常、このプロパティは既存しません。もし既に存在し、それが設定可能でない場合や
O が拡張不可能な場合、[[DefineOwnProperty]] は
7.3.7 CreateNonEnumerableDataPropertyOrThrow ( O, P, V )
抽象操作 CreateNonEnumerableDataPropertyOrThrow は、引数 O（オブジェクト）、P（
アサート : O は通常の拡張可能なオブジェクトで、非設定可能なプロパティを持たない。- newDesc を PropertyDescriptor { [[Value]]:
V, [[Writable]]:
true , [[Enumerable]]:false , [[Configurable]]:true } とする。 - !
DefinePropertyOrThrow (O, P, newDesc) を実行する。 unused を返す。
この抽象操作は、ECMAScript
言語の代入演算子で生成されるプロパティと同じデフォルト属性でプロパティを作成しますが、列挙不可となる点が異なります。通常、このプロパティは既存しません。もし既に存在する場合、
7.3.8 DefinePropertyOrThrow ( O, P, desc )
抽象操作 DefinePropertyOrThrow は、引数 O（オブジェクト）、P（
- success を ? O.[[DefineOwnProperty]](P, desc) とする。
- もし success が
false なら、TypeError 例外を投げる。 unused を返す。
7.3.9 DeletePropertyOrThrow ( O, P )
抽象操作 DeletePropertyOrThrow は、引数 O（オブジェクト）と P（
- success を ? O.[[Delete]](P) とする。
- もし success が
false なら、TypeError 例外を投げる。 unused を返す。
7.3.10 GetMethod ( V, P )
抽象操作 GetMethod は、引数 V（
- func を ?
GetV (V, P) とする。 - もし func が
undefined またはnull なら、undefined を返す。 - もし
IsCallable (func) がfalse なら、TypeError 例外を投げる。 - func を返す。
7.3.11 HasProperty ( O, P )
抽象操作 HasProperty は、引数 O（オブジェクト）と P（
- ? O.[[HasProperty]](P) を返す。
7.3.12 HasOwnProperty ( O, P )
抽象操作 HasOwnProperty は、引数 O（オブジェクト）と P（
- desc を ? O.[[GetOwnProperty]](P) とする。
- もし desc が
undefined ならfalse を返す。 true を返す。
7.3.13 Call ( F, V [ , argumentsList ] )
抽象操作 Call は、引数 F（
- もし argumentsList が省略された場合、argumentsList を新しい空の
リスト に設定する。 - もし
IsCallable (F) がfalse なら、TypeError 例外を投げる。 - ? F.[[Call]](V, argumentsList) を返す。
7.3.14 Construct ( F [ , argumentsList [ , newTarget ] ] )
抽象操作 Construct は、引数 F（
- もし newTarget が省略された場合、newTarget を F に設定する。
- もし argumentsList が省略された場合、argumentsList を新しい空の
リスト に設定する。 - ? F.[[Construct]](argumentsList, newTarget) を返す。
newTarget が省略された場合、この操作は new F(...argumentsList) と同等です。
7.3.15 SetIntegrityLevel ( O, level )
抽象操作 SetIntegrityLevel は、引数 O（オブジェクト）、level（
- status を ? O.[[PreventExtensions]]() とする。
- もし status が
false なら、false を返す。 - keys を ? O.[[OwnPropertyKeys]]() とする。
- もし level が
sealed なら、- keys の各要素 k について、
- ?
DefinePropertyOrThrow (O, k, PropertyDescriptor { [[Configurable]]:false }) を実行する。
- ?
- keys の各要素 k について、
- それ以外の場合、
アサート : level はfrozen である。- keys の各要素 k について、
- currentDesc を ? O.[[GetOwnProperty]](k) とする。
- もし currentDesc が
undefined でなければ、- もし
IsAccessorDescriptor (currentDesc) がtrue なら、- desc を PropertyDescriptor { [[Configurable]]:
false } とする。
- desc を PropertyDescriptor { [[Configurable]]:
- それ以外の場合、
- desc を PropertyDescriptor { [[Configurable]]:
false , [[Writable]]:false } とする。
- desc を PropertyDescriptor { [[Configurable]]:
- ?
DefinePropertyOrThrow (O, k, desc) を実行する。
- もし
true を返す。
7.3.16 TestIntegrityLevel ( O, level )
抽象操作 TestIntegrityLevel は、引数 O（オブジェクト）、level（
- extensible を ?
IsExtensible (O) とする。 - もし extensible が
true なら、false を返す。 - 注：オブジェクトが拡張可能である場合、そのプロパティは検査されません。
- keys を ? O.[[OwnPropertyKeys]]() とする。
- keys の各要素 k について、
- currentDesc を ? O.[[GetOwnProperty]](k) とする。
- もし currentDesc が
undefined でなければ、- もし currentDesc.[[Configurable]] が
true なら、false を返す。 - もし level が
frozen かつIsDataDescriptor (currentDesc) がtrue なら、- もし currentDesc.[[Writable]]
が
true なら、false を返す。
- もし currentDesc.[[Writable]]
が
- もし currentDesc.[[Configurable]] が
true を返す。
7.3.17 CreateArrayFromList ( elements )
抽象操作 CreateArrayFromList は、引数 elements（
- array を !
ArrayCreate (0) とする。 - n を 0 とする。
- elements の各要素 e について、
- !
CreateDataPropertyOrThrow (array, !ToString (𝔽 (n)), e) を実行する。 - n を n + 1 に設定する。
- !
- array を返す。
7.3.18 LengthOfArrayLike ( obj )
抽象操作 LengthOfArrayLike は、引数 obj（オブジェクト）を受け取り、
配列様オブジェクト とは、この操作が
7.3.19 CreateListFromArrayLike ( obj [ , validElementTypes ] )
抽象操作 CreateListFromArrayLike は、引数 obj（
- もし validElementTypes が指定されていなければ、validElementTypes を
all に設定する。 - もし obj が
オブジェクトでない なら、TypeError 例外を投げる。 - len を ?
LengthOfArrayLike (obj) とする。 - list を新しい空の
リスト とする。 - index を 0 とする。
- index < len の間、繰り返し：
- list を返す。
7.3.20 Invoke ( V, P [ , argumentsList ] )
抽象操作 Invoke は、引数 V（
7.3.21 OrdinaryHasInstance ( C, O )
抽象操作 OrdinaryHasInstance は、引数 C（
- もし
IsCallable (C) がfalse なら、false を返す。 - もし C が [[BoundTargetFunction]] 内部スロットを持つなら、
- BC を C.[[BoundTargetFunction]] とする。
- ?
InstanceofOperator (O, BC) を返す。
- もし O が
オブジェクトでない なら、false を返す。 - P を ?
Get (C,"prototype" ) とする。 - もし P が
オブジェクトでない なら、TypeError 例外を投げる。 - 繰り返し：
- O を ? O.[[GetPrototypeOf]]() に設定する。
- もし O が
null なら、false を返す。 - もし
SameValue (P, O) がtrue なら、true を返す。
7.3.22 SpeciesConstructor ( O, defaultConstructor )
抽象操作 SpeciesConstructor は、引数 O（オブジェクト）、defaultConstructor（
- C を ?
Get (O,"constructor" ) とする。 - もし C が
undefined なら、defaultConstructor を返す。 - もし C が
オブジェクトでない なら、TypeError 例外を投げる。 - S を ?
Get (C,%Symbol.species% ) とする。 - もし S が
undefined またはnull なら、defaultConstructor を返す。 - もし
IsConstructor (S) がtrue なら、S を返す。 TypeError 例外を投げる。
7.3.23 EnumerableOwnProperties ( O, kind )
抽象操作 EnumerableOwnProperties は、引数
O（オブジェクト）、kind（
- ownKeys を ? O.[[OwnPropertyKeys]]() とする。
- results を新しい空の
リスト とする。 - ownKeys の各要素 key について：
- もし key が
文字列 なら、- desc を ? O.[[GetOwnProperty]](key) とする。
- もし desc が
undefined でなく、かつ desc.[[Enumerable]] がtrue なら、- もし kind が
key なら、- key を results に追加する。
- それ以外の場合、
- value を ?
Get (O, key) とする。 - もし kind が
value なら、- value を results に追加する。
- それ以外の場合、
アサート : kind はkey+value である。- entry を
CreateArrayFromList («key, value » ) とする。 - entry を results に追加する。
- value を ?
- もし kind が
- もし key が
- results を返す。
7.3.24 GetFunctionRealm ( obj )
抽象操作 GetFunctionRealm は、引数 obj（
- もし obj が [[Realm]] 内部スロットを持つなら、
- obj.[[Realm]] を返す。
- もし obj が
束縛関数エキゾチックオブジェクト なら、- boundTargetFunction を obj.[[BoundTargetFunction]] とする。
- ?
GetFunctionRealm (boundTargetFunction) を返す。
- もし obj が
Proxy エキゾチックオブジェクト なら、- ?
ValidateNonRevokedProxy (obj) を実行する。 - proxyTarget を obj.[[ProxyTarget]] とする。
アサート : proxyTarget は関数オブジェクト である。- ?
GetFunctionRealm (proxyTarget) を返す。
- ?
現在の Realm Record を返す。
ステップ
7.3.25 CopyDataProperties ( target, source, excludedItems )
抽象操作 CopyDataProperties は、引数 target（オブジェクト）、source（
- もし source が
undefined またはnull なら、unused を返す。 - from を !
ToObject (source) とする。 - keys を ? from.[[OwnPropertyKeys]]() とする。
- keys の各要素 nextKey について、
- excluded を
false に設定する。 - excludedItems の各要素 e について、
- もし
SameValue (e, nextKey) がtrue なら、- excluded を
true に設定する。
- excluded を
- もし
- もし excluded が
false なら、- desc を ? from.[[GetOwnProperty]](nextKey) とする。
- もし desc が
undefined でなく、かつ desc.[[Enumerable]] がtrue なら、- propValue を ?
Get (from, nextKey) とする。 - !
CreateDataPropertyOrThrow (target, nextKey, propValue) を実行する。
- propValue を ?
- excluded を
unused を返す。
ここで渡される target は常に新しく作成されたオブジェクトであり、エラーが投げられた場合に直接アクセスすることはできません。
7.3.26 PrivateElementFind ( O, P )
抽象操作 PrivateElementFind は、引数 O（オブジェクト）、P（
- もし O.[[PrivateElements]] が
PrivateElement pe を含み、かつ pe.[[Key]] が P であるなら、- pe を返す。
empty を返す。
7.3.27 PrivateFieldAdd ( O, P, value )
抽象操作 PrivateFieldAdd は、引数 O（オブジェクト）、P（
- もし
ホスト が Webブラウザなら、- ?
HostEnsureCanAddPrivateElement (O) を実行する。
- ?
- entry を
PrivateElementFind (O, P) とする。 - もし entry が
empty でないなら、TypeError 例外を投げる。 PrivateElement { [[Key]]: P, [[Kind]]:field , [[Value]]: value } を O.[[PrivateElements]] に追加する。unused を返す。
7.3.28 PrivateMethodOrAccessorAdd ( O, method )
抽象操作 PrivateMethodOrAccessorAdd は、引数 O（オブジェクト）、method（
アサート : method.[[Kind]] はmethod またはaccessor である。- もし
ホスト が Webブラウザなら、- ?
HostEnsureCanAddPrivateElement (O) を実行する。
- ?
- entry を
PrivateElementFind (O, method.[[Key]]) とする。 - もし entry が
empty でないなら、TypeError 例外を投げる。 - method を O.[[PrivateElements]] に追加する。
unused を返す。
プライベートメソッドおよびアクセサの値はインスタンス間で共有されます。この操作はメソッドやアクセサのコピーを新たに作成しません。
7.3.29 HostEnsureCanAddPrivateElement ( O )
HostEnsureCanAddPrivateElement の実装は以下の要件を満たさなければなりません：
- もし O が
ホスト定義 エキゾチックオブジェクト でなければ、この抽象操作はNormalCompletion (unused ) を返し、他の手順を実行してはならない。 - 同じ引数でこの抽象操作を2回呼び出した場合、同じ種類の
Completion Record を返さなければならない。
HostEnsureCanAddPrivateElement のデフォルト実装は
この抽象操作は ECMAScript の
7.3.30 PrivateGet ( O, P )
抽象操作 PrivateGet は、引数 O（オブジェクト）、P（
- entry を
PrivateElementFind (O, P) とする。 - もし entry が
empty なら、TypeError 例外を投げる。 - もし entry.[[Kind]] が
field またはmethod なら、- entry.[[Value]] を返す。
アサート : entry.[[Kind]] はaccessor である。- もし entry.[[Get]] が
undefined なら、TypeError 例外を投げる。 - getter を entry.[[Get]] とする。
- ?
Call (getter, O) を返す。
7.3.31 PrivateSet ( O, P, value )
抽象操作 PrivateSet は、引数 O（オブジェクト）、P（
- entry を
PrivateElementFind (O, P) とする。 - もし entry が
empty なら、TypeError 例外を投げる。 - もし entry.[[Kind]] が
field なら、- entry.[[Value]] を value に設定する。
- それ以外で entry.[[Kind]] が
method なら、TypeError 例外を投げる。
- それ以外の場合、
unused を返す。
7.3.32 DefineField ( receiver, fieldRecord )
抽象操作 DefineField は、引数 receiver（オブジェクト）、fieldRecord（
- fieldName を fieldRecord.[[Name]] とする。
- initializer を fieldRecord.[[Initializer]] とする。
- もし initializer が
empty でないなら、- initValue を ?
Call (initializer, receiver) とする。
- initValue を ?
- それ以外の場合、
- initValue を
undefined とする。
- initValue を
- もし fieldName が
Private Name なら、- ?
PrivateFieldAdd (receiver, fieldName, initValue) を実行する。
- ?
- それ以外の場合、
アサート : fieldName はプロパティキー である。- ?
CreateDataPropertyOrThrow (receiver, fieldName, initValue) を実行する。
unused を返す。
7.3.33 InitializeInstanceElements ( O, constructor )
抽象操作 InitializeInstanceElements は、引数 O（オブジェクト）、constructor（ECMAScript
- methods を constructor.[[PrivateMethods]] とする。
- methods の各
PrivateElement method について、- ?
PrivateMethodOrAccessorAdd (O, method) を実行する。
- ?
- fields を constructor.[[Fields]] とする。
- fields の各要素 fieldRecord について、
- ?
DefineField (O, fieldRecord) を実行する。
- ?
unused を返す。
7.3.34 AddValueToKeyedGroup ( groups, key, value )
抽象操作 AddValueToKeyedGroup は、引数 groups（
7.3.35 GroupBy ( items, callback, keyCoercion )
抽象操作 GroupBy は、引数 items（
- ?
RequireObjectCoercible (items) を実行する。 - もし
IsCallable (callback) がfalse なら、TypeError 例外を投げる。 - groups を新しい空の
リスト とする。 - iteratorRecord を ?
GetIterator (items,sync ) とする。 - k を 0 とする。
- 繰り返し：
- もし k ≥ 253 - 1 なら、
- error を
ThrowCompletion (新しく作成されたTypeError オブジェクト) とする。 - ?
IteratorClose (iteratorRecord, error) を返す。
- error を
- next を ?
IteratorStepValue (iteratorRecord) とする。 - もし next が
done なら、- groups を返す。
- value を next とする。
- key を
Completion (Call (callback,undefined , « value,𝔽 (k) » )) とする。 IfAbruptCloseIterator (key, iteratorRecord) を実行する。- もし keyCoercion が
property なら、- key を
Completion (ToPropertyKey (key)) に設定する。 IfAbruptCloseIterator (key, iteratorRecord) を実行する。
- key を
- それ以外の場合、
アサート : keyCoercion はcollection である。- key を
CanonicalizeKeyedCollectionKey (key) に設定する。
AddValueToKeyedGroup (groups, key, value) を実行する。- k を k + 1 に設定する。
- もし k ≥ 253 - 1 なら、
7.3.36 SetterThatIgnoresPrototypeProperties ( thisValue, home, p, v )
抽象操作 SetterThatIgnoresPrototypeProperties は、引数 thisValue（
- もし thisValue が
オブジェクトでない なら、TypeError 例外を投げる。
- もし
SameValue (thisValue, home) がtrue なら、 - desc を ? thisValue.[[GetOwnProperty]](p) とする。
- もし desc が
undefined なら、- ?
CreateDataPropertyOrThrow (thisValue, p, v) を実行する。
- ?
- それ以外の場合、
- ?
Set (thisValue, p, v,true ) を実行する。
- ?
unused を返す。
7.4 イテレータオブジェクトに対する操作
共通のイテレーションインターフェース（
7.4.1 イテレータレコード
イテレータレコード とは、next
メソッドをカプセル化するために使用されます。
イテレータレコードは、
| フィールド名 | 値 | 意味 |
|---|---|---|
| [[Iterator]] | オブジェクト |
|
| [[NextMethod]] |
|
[[Iterator]] オブジェクトの next メソッド。
|
| [[Done]] | Boolean |
|
7.4.2 GetIteratorDirect ( obj )
抽象操作 GetIteratorDirect は、引数 obj（オブジェクト）を受け取り、
7.4.3 GetIteratorFromMethod ( obj, method )
抽象操作 GetIteratorFromMethod は、引数 obj（
- iterator を ?
Call (method, obj) とする。 - もし iterator が
オブジェクトでない なら、TypeError 例外を投げる。 - ?
GetIteratorDirect (iterator) を返す。
7.4.4 GetIterator ( obj, kind )
抽象操作 GetIterator は、引数 obj（
- もし kind が
async なら、- method を ?
GetMethod (obj,%Symbol.asyncIterator% ) とする。 - もし method が
undefined なら、- syncMethod を ?
GetMethod (obj,%Symbol.iterator% ) とする。 - もし syncMethod が
undefined なら、TypeError 例外を投げる。 - syncIteratorRecord を ?
GetIteratorFromMethod (obj, syncMethod) とする。 CreateAsyncFromSyncIterator (syncIteratorRecord) を返す。
- syncMethod を ?
- method を ?
- それ以外の場合、
- method を ?
GetMethod (obj,%Symbol.iterator% ) とする。
- method を ?
- もし method が
undefined なら、TypeError 例外を投げる。 - ?
GetIteratorFromMethod (obj, method) を返す。
7.4.5 GetIteratorFlattenable ( obj, primitiveHandling )
抽象操作 GetIteratorFlattenable は、引数 obj（
- もし obj が
オブジェクトでない なら、 - method を ?
GetMethod (obj,%Symbol.iterator% ) とする。 - もし method が
undefined なら、- iterator を obj とする。
- それ以外の場合、
- iterator を ?
Call (method, obj) とする。
- iterator を ?
- もし iterator が
オブジェクトでない なら、TypeError 例外を投げる。 - ?
GetIteratorDirect (iterator) を返す。
7.4.6 IteratorNext ( iteratorRecord [ , value ] )
抽象操作 IteratorNext は、引数 iteratorRecord（
- もし value が指定されていなければ、
- result を
Completion (Call (iteratorRecord.[[NextMethod]], iteratorRecord.[[Iterator]])) とする。
- result を
- それ以外の場合、
- result を
Completion (Call (iteratorRecord.[[NextMethod]], iteratorRecord.[[Iterator]], « value »)) とする。
- result を
- もし result が
throw completion なら、- iteratorRecord.[[Done]] を
true に設定する。 - ? result を返す。
- iteratorRecord.[[Done]] を
- result を ! result に設定する。
- もし result が
オブジェクトでない なら、- iteratorRecord.[[Done]] を
true に設定する。 TypeError 例外を投げる。
- iteratorRecord.[[Done]] を
- result を返す。
7.4.7 IteratorComplete ( iteratorResult )
抽象操作 IteratorComplete は、引数 iteratorResult（オブジェクト）を受け取り、
7.4.8 IteratorValue ( iteratorResult )
抽象操作 IteratorValue は、引数 iteratorResult（オブジェクト）を受け取り、
- ?
Get (iteratorResult,"value" ) を返す。
7.4.9 IteratorStep ( iteratorRecord )
抽象操作 IteratorStep は、引数 iteratorRecord（
- result を ?
IteratorNext (iteratorRecord) とする。 - done を
Completion (IteratorComplete (result)) とする。 - もし done が
throw completion なら、- iteratorRecord.[[Done]] を
true に設定する。 - ? done を返す。
- iteratorRecord.[[Done]] を
- done を ! done に設定する。
- もし done が
true なら、- iteratorRecord.[[Done]] を
true に設定する。 done を返す。
- iteratorRecord.[[Done]] を
- result を返す。
7.4.10 IteratorStepValue ( iteratorRecord )
抽象操作 IteratorStepValue は、引数 iteratorRecord（
- result を ?
IteratorStep (iteratorRecord) とする。 - もし result が
done なら、done を返す。
- value を
Completion (IteratorValue (result)) とする。 - もし value が
throw completion なら、- iteratorRecord.[[Done]] を
true に設定する。
- iteratorRecord.[[Done]] を
- ? value を返す。
7.4.11 IteratorClose ( iteratorRecord, completion )
抽象操作 IteratorClose は、引数 iteratorRecord（
アサート : iteratorRecord.[[Iterator]] がオブジェクト である。- iterator を iteratorRecord.[[Iterator]] とする。
- innerResult を
Completion (GetMethod (iterator,"return" )) とする。 - もし innerResult が
normal completion なら、- return を innerResult.[[Value]] とする。
- もし return が
undefined なら、? completion を返す。 - innerResult を
Completion (Call (return, iterator)) に設定する。
- もし completion が
throw completion なら、? completion を返す。 - もし innerResult が
throw completion なら、? innerResult を返す。 - もし innerResult.[[Value]] が
オブジェクトでない なら、TypeError 例外を投げる。 - ? completion を返す。
7.4.12 IfAbruptCloseIterator ( value, iteratorRecord )
IfAbruptCloseIterator は
IfAbruptCloseIterator (value, iteratorRecord)。
は、次と同じ意味になります：
アサート : value はCompletion Record である。- もし value が
abrupt completion なら、?IteratorClose (iteratorRecord, value) を返す。 - それ以外の場合、value を ! value に設定する。
7.4.13 AsyncIteratorClose ( iteratorRecord, completion )
抽象操作 AsyncIteratorClose は、引数 iteratorRecord（
アサート : iteratorRecord.[[Iterator]] がオブジェクト である。- iterator を iteratorRecord.[[Iterator]] とする。
- innerResult を
Completion (GetMethod (iterator,"return" )) とする。 - もし innerResult が
normal completion なら、- return を innerResult.[[Value]] とする。
- もし return が
undefined なら、? completion を返す。 - innerResult を
Completion (Call (return, iterator)) に設定する。 - もし innerResult が
normal completion なら、innerResult をCompletion (Await (innerResult.[[Value]])) に設定する。
- もし completion が
throw completion なら、? completion を返す。 - もし innerResult が
throw completion なら、? innerResult を返す。 - もし innerResult.[[Value]] が
オブジェクトでない なら、TypeError 例外を投げる。 - ? completion を返す。
7.4.14 CreateIteratorResultObject ( value, done )
抽象操作 CreateIteratorResultObject は、引数 value（
- obj を
OrdinaryObjectCreate (%Object.prototype% ) とする。 - !
CreateDataPropertyOrThrow (obj,"value" , value) を実行する。 - !
CreateDataPropertyOrThrow (obj,"done" , done) を実行する。 - obj を返す。
7.4.15 CreateListIteratorRecord ( list )
抽象操作 CreateListIteratorRecord は、引数 list（
- closure を引数なしで list をキャプチャし、呼び出されたとき以下の手順を実行する新しい
Abstract Closure とする：- list の各要素 E について、
- ?
GeneratorYield (CreateIteratorResultObject (E,false )) を実行する。
- ?
NormalCompletion (undefined ) を返す。
- list の各要素 E について、
- iterator を
CreateIteratorFromClosure (closure,empty ,%Iterator.prototype% ) とする。 イテレータレコード { [[Iterator]]: iterator, [[NextMethod]]: %GeneratorPrototype.next%, [[Done]]:false } を返す。
7.4.16 IteratorToList ( iteratorRecord )
抽象操作 IteratorToList は、引数 iteratorRecord（
- values を新しい空の
リスト とする。 - 繰り返し：
- next を ?
IteratorStepValue (iteratorRecord) とする。 - もし next が
done なら、- values を返す。
- next を values に追加する。
- next を ?
8 構文指向操作
この節で定義されているものに加えて、特化された
8.1 実行時セマンティクス: 評価
8.2 スコープ解析
8.2.1 静的セマンティクス: BoundNames
これは以下の生成規則ごとに分割定義されています：
リスト を返す。その唯一の要素はStringValue であり、識別子 の値である。
- «
"yield" »を返す。
- «
"await" »を返す。
- 新しい空の
リスト を返す。
- names1 を
束縛名 （束縛プロパティリスト について）とする。 - names2 を
束縛名 （束縛残余プロパティ について）とする。 リスト連結 によって names1 と names2 を結合して返す。
- 新しい空の
リスト を返す。
- names1 を
束縛名 （束縛プロパティリスト について）とする。 - names2 を
束縛名 （束縛プロパティ について）とする。 リスト連結 によって names1 と names2 を結合して返す。
BoundNames をBindingIdentifier に対して返す。
- «
"*default*" » を返す。
- 新しい空の
List を返す。
- names1 を
BoundNames のFormalParameterList で取得する。 - names2 を
BoundNames のFunctionRestParameter で取得する。 -
names1 と names2 の
リスト連結 を返す。
- names1 を
BoundNames のFormalParameterList で取得する。 - names2 を
BoundNames のFormalParameter で取得する。 -
names1 と names2 の
リスト連結 を返す。
- formals を
ArrowFormalParameters で、cover されているCoverParenthesizedExpressionAndArrowParameterList から取得する。 - formals の
BoundNames を返す。
BoundNames をBindingIdentifier に対して返す。
- «
"*default*" » を返す。
BoundNames をBindingIdentifier に対して返す。
- «
"*default*" » を返す。
BoundNames をBindingIdentifier に対して返す。
- «
"*default*" » を返す。
BoundNames をBindingIdentifier に対して返す。
- «
"*default*" » を返す。
- head を
AsyncArrowHead で、cover されているCoverCallExpressionAndAsyncArrowHead から取得する。 - head の
BoundNames を返す。
BoundNames をImportClause に対して返す。
- 新しい空の
List を返す。
- names1 を
BoundNames のImportedDefaultBinding で取得する。 - names2 を
BoundNames のNameSpaceImport で取得する。 -
names1 と names2 の
リスト連結 を返す。
- names1 を
BoundNames のImportedDefaultBinding で取得する。 - names2 を
BoundNames のNamedImports で取得する。 -
names1 と names2 の
リスト連結 を返す。
- 新しい空の
List を返す。
- names1 を
BoundNames のImportsList で取得する。 - names2 を
BoundNames のImportSpecifier で取得する。 -
names1 と names2 の
リスト連結 を返す。
BoundNames をImportedBinding に対して返す。
- 新しい空の
List を返す。
BoundNames をVariableStatement に対して返す。
BoundNames をDeclaration に対して返す。
- declarationNames を
BoundNames のHoistableDeclaration で取得する。 - もし declarationNames に
"*default*" 要素が含まれていなければ、"*default*" を declarationNames に追加する。 - declarationNames を返す。
- declarationNames を
BoundNames のClassDeclaration で取得する。 - もし declarationNames に
"*default*" 要素が含まれていなければ、"*default*" を declarationNames に追加する。 - declarationNames を返す。
- «
"*default*" » を返す。
8.2.2 静的セマンティクス：DeclarationPart
FunctionDeclaration を返す。
GeneratorDeclaration を返す。
ClassDeclaration を返す。
LexicalDeclaration を返す。
8.2.3 静的セマンティクス：IsConstantDeclaration
IsConstantDeclaration をLetOrConst に対して返す。
false を返す。
true を返す。
false を返す。
false を返す。
false を返す。
export default
8.2.4 静的セマンティクス：LexicallyDeclaredNames
- 新しい空の
リスト を返す。
- names1 を
LexicallyDeclaredNames のStatementList で取得する。 - names2 を
LexicallyDeclaredNames のStatementListItem で取得する。 -
names1 と names2 の
リスト連結 を返す。
- もし
Statement がStatement ： LabelledStatement LexicallyDeclaredNames のLabelledStatement を返す。 - 新しい空の
リスト を返す。
BoundNames をDeclaration に対して返す。
- 新しい空の
リスト を返す。
- 最初の
CaseClauses が存在する場合、names1 をLexicallyDeclaredNames の最初のCaseClauses で取得する。 - そうでなければ、names1 を新しい空の
リスト とする。 - names2 を
LexicallyDeclaredNames のDefaultClause で取得する。 - 2番目の
CaseClauses が存在する場合、names3 をLexicallyDeclaredNames の2番目のCaseClauses で取得する。 - そうでなければ、names3 を新しい空の
リスト とする。 -
names1、names2、names3 の
リスト連結 を返す。
- names1 を
LexicallyDeclaredNames のCaseClauses で取得する。 - names2 を
LexicallyDeclaredNames のCaseClause で取得する。 -
names1 と names2 の
リスト連結 を返す。
StatementList が存在する場合、LexicallyDeclaredNames のStatementList を返す。- 新しい空の
リスト を返す。
StatementList が存在する場合、LexicallyDeclaredNames のStatementList を返す。- 新しい空の
リスト を返す。
LexicallyDeclaredNames をLabelledItem に対して返す。
- 新しい空の
リスト を返す。
BoundNames をFunctionDeclaration に対して返す。
- 新しい空の
リスト を返す。
TopLevelLexicallyDeclaredNames をStatementList に対して返す。
- 新しい空の
リスト を返す。
TopLevelLexicallyDeclaredNames をStatementList に対して返す。
- 新しい空の
リスト を返す。
- 新しい空の
リスト を返す。
- 新しい空の
リスト を返す。
TopLevelLexicallyDeclaredNames をStatementList に対して返す。
- names1 を
LexicallyDeclaredNames のModuleItemList で取得する。 - names2 を
LexicallyDeclaredNames のModuleItem で取得する。 -
names1 と names2 の
リスト連結 を返す。
BoundNames をImportDeclaration に対して返す。
ExportDeclaration がexportVariableStatement の場合、新しい空のリスト を返す。BoundNames をExportDeclaration に対して返す。
LexicallyDeclaredNames をStatementListItem に対して返す。
8.2.5 静的セマンティクス：LexicallyScopedDeclarations
- declarations1 を
LexicallyScopedDeclarations のStatementList で取得する。 - declarations2 を
LexicallyScopedDeclarations のStatementListItem で取得する。 -
declarations1 と declarations2 の
リスト連結 を返す。
- もし
Statement がStatement ： LabelledStatement LexicallyScopedDeclarations のLabelledStatement を返す。 - 新しい空の
リスト を返す。
リスト （唯一の要素はDeclarationPart ofDeclaration ）を返す。
- 新しい空の
リスト を返す。
- 最初の
CaseClauses が存在する場合、declarations1 をLexicallyScopedDeclarations の最初のCaseClauses で取得する。 - そうでなければ、declarations1 を新しい空の
リスト とする。 - declarations2 を
LexicallyScopedDeclarations のDefaultClause で取得する。 - 2番目の
CaseClauses が存在する場合、declarations3 をLexicallyScopedDeclarations の2番目のCaseClauses で取得する。 - そうでなければ、declarations3 を新しい空の
リスト とする。 -
declarations1、declarations2、declarations3 の
リスト連結 を返す。
- declarations1 を
LexicallyScopedDeclarations のCaseClauses で取得する。 - declarations2 を
LexicallyScopedDeclarations のCaseClause で取得する。 -
declarations1 と declarations2 の
リスト連結 を返す。
StatementList が存在する場合、LexicallyScopedDeclarations のStatementList を返す。- 新しい空の
リスト を返す。
StatementList が存在する場合、LexicallyScopedDeclarations のStatementList を返す。- 新しい空の
リスト を返す。
LexicallyScopedDeclarations をLabelledItem に対して返す。
- 新しい空の
リスト を返す。
- «
FunctionDeclaration » を返す。
- 新しい空の
リスト を返す。
- 新しい空の
リスト を返す。
- 新しい空の
リスト を返す。
- 新しい空の
リスト を返す。
- 新しい空の
リスト を返す。
- 新しい空の
リスト を返す。
- declarations1 を
LexicallyScopedDeclarations のModuleItemList で取得する。 - declarations2 を
LexicallyScopedDeclarations のModuleItem で取得する。 -
declarations1 と declarations2 の
リスト連結 を返す。
- 新しい空の
リスト を返す。
- 新しい空の
リスト を返す。
リスト （唯一の要素はDeclarationPart ofDeclaration ）を返す。
リスト （唯一の要素はDeclarationPart ofHoistableDeclaration ）を返す。
リスト （唯一の要素はClassDeclaration ）を返す。
リスト （唯一の要素はこのExportDeclaration ）を返す。
8.2.6 静的セマンティクス：VarDeclaredNames
- 新しい空の
リスト を返す。
- 新しい空の
リスト を返す。
- names1 を
VarDeclaredNames のStatementList で取得する。 - names2 を
VarDeclaredNames のStatementListItem で取得する。 -
names1 と names2 の
リスト連結 を返す。
- 新しい空の
リスト を返す。
BoundNames をVariableDeclarationList に対して返す。
- names1 を
VarDeclaredNames の 最初のStatement で取得する。 - names2 を
VarDeclaredNames の 2番目のStatement で取得する。 -
names1 と names2 の
リスト連結 を返す。
VarDeclaredNames をStatement に対して返す。
VarDeclaredNames をStatement に対して返す。
VarDeclaredNames をStatement に対して返す。
VarDeclaredNames をStatement に対して返す。
- names1 を
BoundNames のVariableDeclarationList で取得する。 - names2 を
VarDeclaredNames のStatement で取得する。 -
names1 と names2 の
リスト連結 を返す。
VarDeclaredNames をStatement に対して返す。
VarDeclaredNames をStatement に対して返す。
- names1 を
BoundNames のForBinding で取得する。 - names2 を
VarDeclaredNames のStatement で取得する。 -
names1 と names2 の
リスト連結 を返す。
このセクションは付録
VarDeclaredNames をStatement に対して返す。
VarDeclaredNames をCaseBlock に対して返す。
- 新しい空の
リスト を返す。
- 最初の
CaseClauses が存在する場合、names1 をVarDeclaredNames の 最初のCaseClauses で取得する。 - そうでなければ、names1 を新しい空の
リスト とする。 - names2 を
VarDeclaredNames のDefaultClause で取得する。 - 2番目の
CaseClauses が存在する場合、names3 をVarDeclaredNames の 2番目のCaseClauses で取得する。 - そうでなければ、names3 を新しい空の
リスト とする。 -
names1、names2、names3 の
リスト連結 を返す。
- names1 を
VarDeclaredNames のCaseClauses で取得する。 - names2 を
VarDeclaredNames のCaseClause で取得する。 -
names1 と names2 の
リスト連結 を返す。
StatementList が存在する場合、VarDeclaredNames をStatementList に対して返す。- 新しい空の
リスト を返す。
StatementList が存在する場合、VarDeclaredNames をStatementList に対して返す。- 新しい空の
リスト を返す。
VarDeclaredNames をLabelledItem に対して返す。
- 新しい空の
リスト を返す。
- names1 を
VarDeclaredNames のBlock で取得する。 - names2 を
VarDeclaredNames のCatch で取得する。 -
names1 と names2 の
リスト連結 を返す。
- names1 を
VarDeclaredNames のBlock で取得する。 - names2 を
VarDeclaredNames のFinally で取得する。 -
names1 と names2 の
リスト連結 を返す。
- names1 を
VarDeclaredNames のBlock で取得する。 - names2 を
VarDeclaredNames のCatch で取得する。 - names3 を
VarDeclaredNames のFinally で取得する。 -
names1、names2、names3 の
リスト連結 を返す。
VarDeclaredNames をBlock に対して返す。
- 新しい空の
リスト を返す。
TopLevelVarDeclaredNames をStatementList に対して返す。
- 新しい空の
リスト を返す。
TopLevelVarDeclaredNames をStatementList に対して返す。
- 新しい空の
リスト を返す。
- 新しい空の
リスト を返す。
- 新しい空の
リスト を返す。
TopLevelVarDeclaredNames をStatementList に対して返す。
- names1 を
VarDeclaredNames のModuleItemList で取得する。 - names2 を
VarDeclaredNames のModuleItem で取得する。 -
names1 と names2 の
リスト連結 を返す。
- 新しい空の
リスト を返す。
ExportDeclaration がexportVariableStatement の場合、BoundNames をExportDeclaration に対して返す。- 新しい空の
リスト を返す。
8.2.7 静的セマンティクス：VarScopedDeclarations
- 新しい空の
リスト を返す。
- 新しい空の
リスト を返す。
- declarations1 を
VarScopedDeclarations のStatementList で取得する。 - declarations2 を
VarScopedDeclarations のStatementListItem で取得する。 -
declarations1 と declarations2 の
リスト連結 を返す。
- 新しい空の
リスト を返す。
- «
VariableDeclaration » を返す。
- declarations1 を
VarScopedDeclarations のVariableDeclarationList で取得する。 -
declarations1 と «
VariableDeclaration » のリスト連結 を返す。
- declarations1 を
VarScopedDeclarations の最初のStatement で取得する。 - declarations2 を
VarScopedDeclarations の2番目のStatement で取得する。 -
declarations1 と declarations2 の
リスト連結 を返す。
VarScopedDeclarations をStatement に対して返す。
VarScopedDeclarations をStatement に対して返す。
VarScopedDeclarations をStatement に対して返す。
VarScopedDeclarations をStatement に対して返す。
- declarations1 を
VarScopedDeclarations のVariableDeclarationList で取得する。 - declarations2 を
VarScopedDeclarations のStatement で取得する。 -
declarations1 と declarations2 の
リスト連結 を返す。
VarScopedDeclarations をStatement に対して返す。
VarScopedDeclarations をStatement に対して返す。
- declarations1 を «
ForBinding » とする。 - declarations2 を
VarScopedDeclarations のStatement で取得する。 -
declarations1 と declarations2 の
リスト連結 を返す。
このセクションは付属書
VarScopedDeclarations をStatement に対して返す。
VarScopedDeclarations をCaseBlock に対して返す。
- 新しい空の
リスト を返す。
- 最初の
CaseClauses が存在する場合、declarations1 をVarScopedDeclarations の最初のCaseClauses で取得する。 - そうでなければ、declarations1 を新しい空の
リスト とする。 - declarations2 を
VarScopedDeclarations のDefaultClause で取得する。 - 2番目の
CaseClauses が存在する場合、declarations3 をVarScopedDeclarations の2番目のCaseClauses で取得する。 - そうでなければ、declarations3 を新しい空の
リスト とする。 -
declarations1、declarations2、declarations3 の
リスト連結 を返す。
- declarations1 を
VarScopedDeclarations のCaseClauses で取得する。 - declarations2 を
VarScopedDeclarations のCaseClause で取得する。 -
declarations1 と declarations2 の
リスト連結 を返す。
StatementList が存在する場合、VarScopedDeclarations のStatementList を返す。- 新しい空の
リスト を返す。
StatementList が存在する場合、VarScopedDeclarations のStatementList を返す。- 新しい空の
リスト を返す。
VarScopedDeclarations をLabelledItem に対して返す。
- 新しい空の
リスト を返す。
- declarations1 を
VarScopedDeclarations のBlock で取得する。 - declarations2 を
VarScopedDeclarations のCatch で取得する。 -
declarations1 と declarations2 の
リスト連結 を返す。
- declarations1 を
VarScopedDeclarations のBlock で取得する。 - declarations2 を
VarScopedDeclarations のFinally で取得する。 -
declarations1 と declarations2 の
リスト連結 を返す。
- declarations1 を
VarScopedDeclarations のBlock で取得する。 - declarations2 を
VarScopedDeclarations のCatch で取得する。 - declarations3 を
VarScopedDeclarations のFinally で取得する。 -
declarations1、declarations2、declarations3 の
リスト連結 を返す。
VarScopedDeclarations をBlock に対して返す。
- 新しい空の
リスト を返す。
TopLevelVarScopedDeclarations をStatementList に対して返す。
- 新しい空の
リスト を返す。
TopLevelVarScopedDeclarations をStatementList に対して返す。
- 新しい空の
リスト を返す。
- 新しい空の
リスト を返す。
- 新しい空の
リスト を返す。
TopLevelVarScopedDeclarations をStatementList に対して返す。
- 新しい空の
リスト を返す。
- declarations1 を
VarScopedDeclarations のModuleItemList で取得する。 - declarations2 を
VarScopedDeclarations のModuleItem で取得する。 -
declarations1 と declarations2 の
リスト連結 を返す。
- 新しい空の
リスト を返す。
ExportDeclaration がexportVariableStatement の場合、VarScopedDeclarations をVariableStatement に対して返す。- 新しい空の
リスト を返す。
8.2.8 静的セマンティクス：TopLevelLexicallyDeclaredNames
- names1を、
TopLevelLexicallyDeclaredNames のStatementList に対する値とする。 - names2を、
TopLevelLexicallyDeclaredNames のStatementListItem に対する値とする。 リスト連結 で names1とnames2を返す。
- 新しい空の
リスト を返す。
- もし
Declaration がDeclaration : HoistableDeclaration - 新しい空の
リスト を返す。
- 新しい空の
BoundNames のDeclaration に対する値を返す。
関数またはスクリプトのトップレベルでは、function宣言はレキシカル宣言ではなくvar宣言として扱われる。
8.2.9 静的セマンティクス：TopLevelLexicallyScopedDeclarations
- declarations1を、
TopLevelLexicallyScopedDeclarations のStatementList に対する値とする。 - declarations2を、
TopLevelLexicallyScopedDeclarations のStatementListItem に対する値とする。 リスト連結 で declarations1とdeclarations2を返す。
- 新しい空の
リスト を返す。
- もし
Declaration がDeclaration : HoistableDeclaration - 新しい空の
リスト を返す。
- 新しい空の
- «
Declaration » を返す。
8.2.10 静的セマンティクス：TopLevelVarDeclaredNames
- names1を、
TopLevelVarDeclaredNames のStatementList に対する値とする。 - names2を、
TopLevelVarDeclaredNames のStatementListItem に対する値とする。 リスト連結 で names1とnames2を返す。
- もし
Declaration がDeclaration : HoistableDeclaration BoundNames のHoistableDeclaration に対する値を返す。
- 新しい空の
リスト を返す。
- もし
Statement がStatement : LabelledStatement TopLevelVarDeclaredNames のStatement に対する値を返す。 VarDeclaredNames のStatement に対する値を返す。
関数やスクリプトのトップレベルでは、内部のfunction宣言はvar宣言として扱われる。
TopLevelVarDeclaredNames のLabelledItem に対する値を返す。
- もし
Statement がStatement : LabelledStatement TopLevelVarDeclaredNames のStatement に対する値を返す。 VarDeclaredNames のStatement に対する値を返す。
BoundNames のFunctionDeclaration に対する値を返す。
8.2.11 静的セマンティクス：TopLevelVarScopedDeclarations
- declarations1を、
TopLevelVarScopedDeclarations のStatementList に対する値とする。 - declarations2を、
TopLevelVarScopedDeclarations のStatementListItem に対する値とする。 リスト連結 で declarations1とdeclarations2を返す。
- もし
Statement がStatement : LabelledStatement TopLevelVarScopedDeclarations のStatement に対する値を返す。 VarScopedDeclarations のStatement に対する値を返す。
- もし
Declaration がDeclaration : HoistableDeclaration - declarationを
DeclarationPart のHoistableDeclaration に対する値とする。 - « declaration » を返す。
- declarationを
- 新しい空の
リスト を返す。
TopLevelVarScopedDeclarations のLabelledItem に対する値を返す。
- もし
Statement がStatement : LabelledStatement TopLevelVarScopedDeclarations のStatement に対する値を返す。 VarScopedDeclarations のStatement に対する値を返す。
- «
FunctionDeclaration » を返す。
8.3 ラベル
8.3.1 静的セマンティクス：ContainsDuplicateLabels
false を返す。
- hasDuplicatesを
ContainsDuplicateLabels のStatementList にlabelSetを引数として適用した結果とする。 - もしhasDuplicatesが
true なら、true を返す。 ContainsDuplicateLabels のStatementListItem にlabelSetを引数として適用した結果を返す。
- hasDuplicateを、最初の
Statement にlabelSetを引数としてContainsDuplicateLabels を適用した結果とする。 - もしhasDuplicateが
true なら、true を返す。 - 2番目の
Statement にlabelSetを引数としてContainsDuplicateLabels を適用した結果を返す。
ContainsDuplicateLabels をStatement にlabelSetを引数として適用した結果を返す。
ContainsDuplicateLabels をStatement にlabelSetを引数として適用した結果を返す。
ContainsDuplicateLabels をStatement にlabelSetを引数として適用した結果を返す。
ContainsDuplicateLabels をStatement にlabelSetを引数として適用した結果を返す。
ContainsDuplicateLabels のStatement にlabelSetを引数として適用した結果を返す。
このセクションは付録
ContainsDuplicateLabels をStatement にlabelSetを引数として適用した結果を返す。
ContainsDuplicateLabels をCaseBlock にlabelSetを引数として適用した結果を返す。
false を返す。
- 最初の
CaseClauses が存在する場合、- 最初の
CaseClauses にlabelSetを引数としてContainsDuplicateLabels を適用した結果がtrue なら、true を返す。
- 最初の
DefaultClause にlabelSetを引数としてContainsDuplicateLabels を適用した結果がtrue なら、true を返す。- 2番目の
CaseClauses が存在しなければ、false を返す。 - 2番目の
CaseClauses にlabelSetを引数としてContainsDuplicateLabels を適用した結果を返す。
- hasDuplicatesを
ContainsDuplicateLabels のCaseClauses にlabelSetを引数として適用した結果とする。 - もしhasDuplicatesが
true なら、true を返す。 ContainsDuplicateLabels をCaseClause にlabelSetを引数として適用した結果を返す。
StatementList が存在する場合、ContainsDuplicateLabels をStatementList にlabelSetを引数として適用した結果を返す。false を返す。
StatementList が存在する場合、ContainsDuplicateLabels をStatementList にlabelSetを引数として適用した結果を返す。false を返す。
- labelを
LabelIdentifier のStringValue とする。 - もしlabelSetがlabelを含むなら、
true を返す。 - newLabelSetを
list-concatenation によりlabelSetと« label »の連結とする。 ContainsDuplicateLabels をLabelledItem にnewLabelSetを引数として適用した結果を返す。
false を返す。
- hasDuplicates に
ContainsDuplicateLabels のブロック と引数 labelSet を設定する。 - hasDuplicates が
true の場合、true を返す。 ContainsDuplicateLabels のcatch節 と引数 labelSet を返す。
- hasDuplicates に
ContainsDuplicateLabels のブロック と引数 labelSet を設定する。 - hasDuplicates が
true の場合、true を返す。 ContainsDuplicateLabels のfinally節 と引数 labelSet を返す。
ContainsDuplicateLabels のブロック と引数 labelSet がtrue の場合、true を返す。ContainsDuplicateLabels のcatch節 と引数 labelSet がtrue の場合、true を返す。ContainsDuplicateLabels のfinally節 と引数 labelSet を返す。
ContainsDuplicateLabels のブロック と引数 labelSet を返す。
false を返す。
false を返す。
- hasDuplicates に
ContainsDuplicateLabels のモジュール項目リスト と引数 labelSet を設定する。 - hasDuplicates が
true の場合、true を返す。 ContainsDuplicateLabels のモジュール項目 と引数 labelSet を返す。
false を返す。
8.3.2 静的セマンティクス: ContainsUndefinedBreakTarget
false を返す。
- hasUndefinedLabels に
ContainsUndefinedBreakTarget ofStatementList を引数 labelSet で適用した結果を代入する。 - もし hasUndefinedLabels が
true なら、true を返す。 ContainsUndefinedBreakTarget ofStatementListItem を引数 labelSet で適用した結果を返す。
- hasUndefinedLabels に、最初の
Statement に labelSet を渡してContainsUndefinedBreakTarget を適用した結果を代入する。 - もし hasUndefinedLabels が
true なら、true を返す。 - 2つ目の
Statement に labelSet を渡してContainsUndefinedBreakTarget を適用した結果を返す。
ContainsUndefinedBreakTarget をStatement に labelSet を渡して適用した結果を返す。
ContainsUndefinedBreakTarget をStatement に labelSet を渡して適用した結果を返す。
ContainsUndefinedBreakTarget をStatement に labelSet を渡して適用した結果を返す。
ContainsUndefinedBreakTarget をStatement に labelSet を渡して適用した結果を返す。
ContainsUndefinedBreakTarget をStatement に labelSet を渡して適用した結果を返す。
本節は付録
false を返す。
- もし labelSet に
LabelIdentifier のStringValue が含まれていなければ、true を返す。 false を返す。
ContainsUndefinedBreakTarget をStatement に labelSet を渡して適用した結果を返す。
ContainsUndefinedBreakTarget をCaseBlock に labelSet を渡して適用した結果を返す。
false を返す。
- 最初の
CaseClauses が存在する場合、- もし
ContainsUndefinedBreakTarget of 最初のCaseClauses に labelSet を渡して適用した結果がtrue なら、true を返す。
- もし
ContainsUndefinedBreakTarget ofDefaultClause に labelSet を渡して適用した結果がtrue なら、true を返す。- 2つ目の
CaseClauses が存在しない場合、false を返す。 ContainsUndefinedBreakTarget of 2つ目のCaseClauses に labelSet を渡して適用した結果を返す。
- hasUndefinedLabels に
ContainsUndefinedBreakTarget ofCaseClauses に labelSet を渡して適用した結果を代入する。 - もし hasUndefinedLabels が
true なら、true を返す。 ContainsUndefinedBreakTarget ofCaseClause に labelSet を渡して適用した結果を返す。
StatementList が存在する場合、ContainsUndefinedBreakTarget ofStatementList に labelSet を渡して適用した結果を返す。false を返す。
StatementList が存在する場合、ContainsUndefinedBreakTarget ofStatementList に labelSet を渡して適用した結果を返す。false を返す。
- label に
LabelIdentifier のStringValue を代入する。 - newLabelSet に
labelSet と « label » のリスト連結を代入する。 ContainsUndefinedBreakTarget をLabelledItem に newLabelSet を渡して適用した結果を返す。
false を返す。
- hasUndefinedLabels に
ContainsUndefinedBreakTarget ofBlock に labelSet を渡して適用した結果を代入する。 - もし hasUndefinedLabels が
true なら、true を返す。 ContainsUndefinedBreakTarget ofCatch に labelSet を渡して適用した結果を返す。
- hasUndefinedLabels に
ContainsUndefinedBreakTarget ofBlock に labelSet を渡して適用した結果を代入する。 - もし hasUndefinedLabels が
true なら、true を返す。 ContainsUndefinedBreakTarget ofFinally に labelSet を渡して適用した結果を返す。
ContainsUndefinedBreakTarget ofBlock に labelSet を渡して適用した結果がtrue なら、true を返す。ContainsUndefinedBreakTarget ofCatch に labelSet を渡して適用した結果がtrue なら、true を返す。ContainsUndefinedBreakTarget ofFinally に labelSet を渡して適用した結果を返す。
ContainsUndefinedBreakTarget ofBlock に labelSet を渡して適用した結果を返す。
false を返す。
false を返す。
- hasUndefinedLabels に
ContainsUndefinedBreakTarget ofModuleItemList に labelSet を渡して適用した結果を代入する。 - もし hasUndefinedLabels が
true なら、true を返す。 ContainsUndefinedBreakTarget ofModuleItem に labelSet を渡して適用した結果を返す。
false を返す。
8.3.3 静的セマンティクス: ContainsUndefinedContinueTarget
false を返す。
ContainsUndefinedContinueTarget をBlockStatement に iterationSet および « » を渡して適用した結果を返す。
- newIterationSet に
iterationSet と labelSet のリスト連結を代入する。 ContainsUndefinedContinueTarget をIterationStatement に newIterationSet および « » を渡して適用した結果を返す。
- hasUndefinedLabels に
ContainsUndefinedContinueTarget ofStatementList に iterationSet および « » を渡して適用した結果を代入する。 - もし hasUndefinedLabels が
true なら、true を返す。 ContainsUndefinedContinueTarget ofStatementListItem に iterationSet および « » を渡して適用した結果を返す。
- hasUndefinedLabels に
ContainsUndefinedContinueTarget of 最初のStatement に iterationSet および « » を渡して適用した結果を代入する。 - もし hasUndefinedLabels が
true なら、true を返す。 - 2つ目の
Statement に iterationSet および « » を渡してContainsUndefinedContinueTarget を適用した結果を返す。
ContainsUndefinedContinueTarget をStatement に iterationSet および « » を渡して適用した結果を返す。
ContainsUndefinedContinueTarget をStatement に iterationSet および « » を渡して適用した結果を返す。
ContainsUndefinedContinueTarget をStatement に iterationSet および « » を渡して適用した結果を返す。
ContainsUndefinedContinueTarget をStatement に iterationSet および « » を渡して適用した結果を返す。
ContainsUndefinedContinueTarget をStatement に iterationSet および « » を渡して適用した結果を返す。
本節は付録
false を返す。
- もし iterationSet に
LabelIdentifier のStringValue が含まれていなければ、true を返す。 false を返す。
ContainsUndefinedContinueTarget をStatement に iterationSet および « » を渡して適用した結果を返す。
ContainsUndefinedContinueTarget をCaseBlock に iterationSet および « » を渡して適用した結果を返す。
false を返す。
- 最初の
CaseClauses が存在する場合、- もし
ContainsUndefinedContinueTarget of 最初のCaseClauses に iterationSet および « » を渡して適用した結果がtrue なら、true を返す。
- もし
ContainsUndefinedContinueTarget ofDefaultClause に iterationSet および « » を渡して適用した結果がtrue なら、true を返す。- 2つ目の
CaseClauses が存在しない場合、false を返す。 ContainsUndefinedContinueTarget of 2つ目のCaseClauses に iterationSet および « » を渡して適用した結果を返す。
- hasUndefinedLabels に
ContainsUndefinedContinueTarget ofCaseClauses に iterationSet および « » を渡して適用した結果を代入する。 - もし hasUndefinedLabels が
true なら、true を返す。 ContainsUndefinedContinueTarget ofCaseClause に iterationSet および « » を渡して適用した結果を返す。
StatementList が存在する場合、ContainsUndefinedContinueTarget ofStatementList に iterationSet および « » を渡して適用した結果を返す。false を返す。
StatementList が存在する場合、ContainsUndefinedContinueTarget ofStatementList に iterationSet および « » を渡して適用した結果を返す。false を返す。
- label に
LabelIdentifier のStringValue を代入する。 - newLabelSet に
labelSet と « label » のリスト連結を代入する。 ContainsUndefinedContinueTarget をLabelledItem に iterationSet および newLabelSet を渡して適用した結果を返す。
false を返す。
- hasUndefinedLabels に
ContainsUndefinedContinueTarget ofBlock に iterationSet および « » を渡して適用した結果を代入する。 - もし hasUndefinedLabels が
true なら、true を返す。 ContainsUndefinedContinueTarget ofCatch に iterationSet および « » を渡して適用した結果を返す。
- hasUndefinedLabels に
ContainsUndefinedContinueTarget ofBlock に iterationSet および « » を渡して適用した結果を代入する。 - もし hasUndefinedLabels が
true なら、true を返す。 ContainsUndefinedContinueTarget ofFinally に iterationSet および « » を渡して適用した結果を返す。
ContainsUndefinedContinueTarget ofBlock に iterationSet および « » を渡して適用した結果がtrue なら、true を返す。ContainsUndefinedContinueTarget ofCatch に iterationSet および « » を渡して適用した結果がtrue なら、true を返す。ContainsUndefinedContinueTarget ofFinally に iterationSet および « » を渡して適用した結果を返す。
ContainsUndefinedContinueTarget ofBlock に iterationSet および « » を渡して適用した結果を返す。
false を返す。
false を返す。
- hasUndefinedLabels に
ContainsUndefinedContinueTarget ofModuleItemList に iterationSet および « » を渡して適用した結果を代入する。 - もし hasUndefinedLabels が
true なら、true を返す。 ContainsUndefinedContinueTarget ofModuleItem に iterationSet および « » を渡して適用した結果を返す。
false を返す。
8.4 関数名の推論
8.4.1 静的セマンティクス: HasName
- expr を
ParenthesizedExpression （CoverParenthesizedExpressionAndArrowParameterList によってカバーされている もの）とする。 IsFunctionDefinition of expr がfalse なら、false を返す。HasName of expr を返す。
false を返す。
true を返す。
8.4.2 静的セマンティクス: IsFunctionDefinition
- expr を
ParenthesizedExpression （CoverParenthesizedExpressionAndArrowParameterList によりカバーされている もの）とする。 IsFunctionDefinition of expr を返す。
false を返す。
true を返す。
8.4.3 静的セマンティクス: IsAnonymousFunctionDefinition (expr)
抽象オペレーション IsAnonymousFunctionDefinition は引数 expr（
IsFunctionDefinition of expr がfalse なら、false を返す。- hasName に
HasName of expr を代入する。 - hasName が
true なら、false を返す。 true を返す。
8.4.4 静的セマンティクス: IsIdentifierRef
true を返す。
false を返す。
8.4.5 実行時セマンティクス: NamedEvaluation
- expr を
ParenthesizedExpression （CoverParenthesizedExpressionAndArrowParameterList によりカバーされている もの）とする。 - ?
NamedEvaluation of expr に引数 name を渡して返す。
アサート :IsAnonymousFunctionDefinition (Expression ) がtrue であること。- ?
NamedEvaluation ofExpression に引数 name を渡して返す。
InstantiateOrdinaryFunctionExpression ofFunctionExpression に引数 name を渡して返す。
InstantiateGeneratorFunctionExpression ofGeneratorExpression に引数 name を渡して返す。
InstantiateAsyncGeneratorFunctionExpression ofAsyncGeneratorExpression に引数 name を渡して返す。
InstantiateAsyncFunctionExpression ofAsyncFunctionExpression に引数 name を渡して返す。
InstantiateArrowFunctionExpression ofArrowFunction に引数 name を渡して返す。
InstantiateAsyncArrowFunctionExpression ofAsyncArrowFunction に引数 name を渡して返す。
- value に ?
ClassDefinitionEvaluation ofClassTail に引数undefined と name を渡して返す。 - value.[[SourceText]] に
ClassExpression にマッチしたソーステキストを設定する。 - value を返す。
8.5 含む
8.5.1 静的セマンティクス: Contains
本仕様において、以下に列挙されていないすべての文法生成規則の選択肢は、暗黙的に次のデフォルトのContains定義を持つ：
false を返す。
サブ構造に依存する静的セマンティクス規則は、一般的に関数定義の内部は調べない。
- もしsymbolが
ClassBody であれば、true を返す。 - もしsymbolが
ClassHeritage であれば、- もし
ClassHeritage が存在すればtrue 、そうでなければfalse を返す。
- もし
- もし
ClassHeritage が存在すれば、- もし
ClassHeritage Contains symbolがtrue であれば、true を返す。
- もし
ComputedPropertyContains をClassBody と引数symbolで呼び出した結果を返す。
サブ構造に依存する静的セマンティクス規則は、一般的にクラス本体の内部は
false を返す。
サブ構造に依存する静的セマンティクス規則は、一般的にstatic 初期化ブロックの内部は調べない。
- もしsymbolが
NewTarget 、SuperProperty 、SuperCall 、super、またはthisのいずれでもなければ、false を返す。 - もし
ArrowParameters Contains symbol がtrue であれば、true を返す。 ConciseBody Contains symbolの結果を返す。
- formalsを
ArrowFormalParameters とし、それは被覆 されているCoverParenthesizedExpressionAndArrowParameterList に対応する。 - formals
Contains symbolの結果を返す。
- もしsymbolが
NewTarget 、SuperProperty 、SuperCall 、super、またはthisのいずれでもなければ、false を返す。 AsyncConciseBody Contains symbolの結果を返す。
- もしsymbolが
NewTarget 、SuperProperty 、SuperCall 、super、またはthisのいずれでもなければ、false を返す。 - headを
AsyncArrowHead とし、それは被覆 されているCoverCallExpressionAndAsyncArrowHead に対応する。 - もしhead
Contains symbol がtrue であれば、true を返す。 AsyncConciseBody Contains symbolの結果を返す。
Containsはnew.target、this、およびsuperの使用を検出するために利用される。
- もしsymbolが
MethodDefinition であれば、true を返す。 ComputedPropertyContains をMethodDefinition と引数symbolで呼び出した結果を返す。
false を返す。
- もし
MemberExpression Contains symbol がtrue であれば、true を返す。 false を返す。
- もしsymbolが
ReservedWord superであれば、true を返す。 false を返す。
- もし
CallExpression Contains symbol がtrue であれば、true を返す。 false を返す。
false を返す。
- もし
OptionalChain Contains symbol がtrue であれば、true を返す。 false を返す。
8.5.2 静的セマンティクス: ComputedPropertyContains
false を返す。
ComputedPropertyName Contains symbolの結果を返す。
ComputedPropertyContains をClassElementName と引数symbolで呼び出した結果を返す。
ComputedPropertyContains をClassElementName と引数symbolで呼び出した結果を返す。
ComputedPropertyContains をClassElementName と引数symbolで呼び出した結果を返す。
- inListを
ComputedPropertyContains をClassElementList と引数symbolで呼び出した結果とする。 - もしinListが
true であれば、true を返す。 ComputedPropertyContains をClassElement と引数symbolで呼び出した結果を返す。
false を返す。
false を返す。
ComputedPropertyContains をClassElementName と引数symbolで呼び出した結果を返す。
ComputedPropertyContains をClassElementName と引数symbolで呼び出した結果を返す。
8.6 その他
これらの操作は、仕様書の複数の箇所で使用されます。
8.6.1 実行時セマンティクス: InstantiateFunctionObject
-
InstantiateOrdinaryFunctionObject をFunctionDeclaration 、引数 env および privateEnv で呼び出した結果を返す。
-
InstantiateGeneratorFunctionObject をGeneratorDeclaration 、引数 env および privateEnv で呼び出した結果を返す。
-
InstantiateAsyncGeneratorFunctionObject をAsyncGeneratorDeclaration 、引数 env および privateEnv で呼び出した結果を返す。
-
InstantiateAsyncFunctionObject をAsyncFunctionDeclaration 、引数 env および privateEnv で呼び出した結果を返す。
8.6.2 実行時セマンティクス: BindingInitialization
これは以下の生成規則ごとに定義される:
-
name を
StringValue （Identifier の）とする。 -
InitializeBoundName (name, value, environment) を実行し、その結果を返す（?付き）。
-
InitializeBoundName ("yield" , value, environment) を実行し、その結果を返す（?付き）。
-
InitializeBoundName ("await" , value, environment) を実行し、その結果を返す（?付き）。
-
?
RequireObjectCoercible (value) を実行する。 -
BindingInitialization ofObjectBindingPattern （引数 value と environment） を実行し、その結果を返す（?付き）。
-
iteratorRecord を
?
GetIterator (value,sync ) とする。 -
result を
Completion (IteratorBindingInitialization ofArrayBindingPattern （引数 iteratorRecord と environment）) とする。 -
iteratorRecord.[[Done]] が
false の場合、?IteratorClose (iteratorRecord, result) を返す。 - ? result を返す。
unused を返す。
-
?
PropertyBindingInitialization ofBindingPropertyList （引数 value と environment）を実行する。 unused を返す。
-
excludedNames を新しい空の
List とする。 -
RestBindingInitialization ofBindingRestProperty （引数 value, environment, excludedNames） を実行し、その結果を返す（?付き）。
-
excludedNames を
?
PropertyBindingInitialization ofBindingPropertyList （引数 value と environment）の結果とする。 -
RestBindingInitialization ofBindingRestProperty （引数 value, environment, excludedNames） を実行し、その結果を返す（?付き）。
8.6.2.1 InitializeBoundName ( name, value, environment )
抽象操作 InitializeBoundName は、引数 name（文字列）、value（
-
environment が
undefined でない場合、- ! environment.InitializeBinding(name, value) を実行する。
unused を返す。
- それ以外の場合、
-
lhs を
?
ResolveBinding (name) とする。 -
?
PutValue (lhs, value) を返す。
-
lhs を
?
8.6.3 実行時セマンティクス: IteratorBindingInitialization
これは以下の生成規則ごとに定義される:
unused を返す。
-
?
IteratorDestructuringAssignmentEvaluation ofElision （引数 iteratorRecord） を実行し、その結果を返す。
-
Elision が存在する場合、-
?
IteratorDestructuringAssignmentEvaluation ofElision （引数 iteratorRecord） を実行する。
-
?
-
?
IteratorBindingInitialization ofBindingRestElement （引数 iteratorRecord および environment）を実行し、その結果を返す。
-
?
IteratorBindingInitialization ofBindingElementList （引数 iteratorRecord および environment）を実行する。 -
?
IteratorDestructuringAssignmentEvaluation ofElision （引数 iteratorRecord） を実行し、その結果を返す。
-
?
IteratorBindingInitialization ofBindingElementList （引数 iteratorRecord および environment）を実行する。 -
Elision が存在する場合、-
?
IteratorDestructuringAssignmentEvaluation ofElision （引数 iteratorRecord） を実行する。
-
?
-
?
IteratorBindingInitialization ofBindingRestElement （引数 iteratorRecord および environment）を実行し、その結果を返す。
-
?
IteratorBindingInitialization ofBindingElementList （引数 iteratorRecord および environment）を実行する。 -
?
IteratorBindingInitialization ofBindingElisionElement （引数 iteratorRecord および environment）を実行し、その結果を返す。
-
?
IteratorDestructuringAssignmentEvaluation ofElision （引数 iteratorRecord） を実行する。 -
?
IteratorBindingInitialization ofBindingElement （引数 iteratorRecord および environment）を実行し、その結果を返す。
-
bindingId を
StringValue ofBindingIdentifier とする。 -
lhs を
?
ResolveBinding (bindingId, environment) とする。 - v を
undefined とする。 -
iteratorRecord.[[Done]] が
false の場合、-
next を
?
IteratorStepValue (iteratorRecord) とする。 -
next が
done でない場合、- v に next を設定する。
-
next を
?
-
Initializer が存在し、 v がundefined の場合、-
IsAnonymousFunctionDefinition (Initializer ) がtrue の場合、-
v に
?
NamedEvaluation ofInitializer （引数 bindingId ）の結果を設定する。
-
v に
?
-
それ以外の場合、
-
defaultValue を
?
Evaluation ofInitializer の結果とする。 -
v に
?
GetValue (defaultValue) の結果を設定する。
-
defaultValue を
?
-
-
environment が
undefined の場合、 ?PutValue (lhs, v) を返す。 -
?
InitializeReferencedBinding (lhs, v) を返す。
- v を
undefined とする。 -
iteratorRecord.[[Done]] が
false の場合、-
next を
?
IteratorStepValue (iteratorRecord) とする。 -
next が
done でない場合、- v に next を設定する。
-
next を
?
-
Initializer が存在し、 v がundefined の場合、-
defaultValue を
?
Evaluation ofInitializer の結果とする。 -
v に
?
GetValue (defaultValue) の結果を設定する。
-
defaultValue を
?
-
?
BindingInitialization ofBindingPattern （引数 v および environment）を実行し、その結果を返す。
-
lhs を
?
ResolveBinding (StringValue ofBindingIdentifier , environment) とする。 -
A を
!
ArrayCreate (0) とする。 - n を 0 とする。
-
繰り返し、
- next を
done とする。 -
iteratorRecord.[[Done]] が
false の場合、-
next に
?
IteratorStepValue (iteratorRecord) を設定する。
-
next に
?
-
next が
done の場合、-
environment が
undefined なら ?PutValue (lhs, A) を返す。 -
?
InitializeReferencedBinding (lhs, A) を返す。
-
environment が
-
!
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), next) を実行する。 - n を n + 1 に設定する。
- next を
-
A を
!
ArrayCreate (0) とする。 - n を 0 とする。
-
繰り返し、
- next を
done とする。 -
iteratorRecord.[[Done]] が
false の場合、-
next に
?
IteratorStepValue (iteratorRecord) を設定する。
-
next に
?
-
next が
done の場合、-
?
BindingInitialization ofBindingPattern （引数 A および environment）を実行し、その結果を返す。
-
?
-
!
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), next) を実行する。 - n を n + 1 に設定する。
- next を
unused を返す。
-
?
IteratorBindingInitialization ofFormalParameterList （引数 iteratorRecord および environment）を実行する。 -
?
IteratorBindingInitialization ofFunctionRestParameter （引数 iteratorRecord および environment）を実行し、その結果を返す。
-
?
IteratorBindingInitialization ofFormalParameterList （引数 iteratorRecord および environment）を実行する。 -
?
IteratorBindingInitialization ofFormalParameter （引数 iteratorRecord および environment）を実行し、その結果を返す。
- v を
undefined とする。 -
Assert : iteratorRecord.[[Done]] はfalse である。 -
next を
?
IteratorStepValue (iteratorRecord) とする。 -
next が
done でない場合、- v に next を設定する。
-
?
BindingInitialization ofBindingIdentifier （引数 v および environment）を実行し、その結果を返す。
-
formals を
ArrowFormalParameters （CoverParenthesizedExpressionAndArrowParameterList によりcover される）とする。 -
?
IteratorBindingInitialization of formals（引数 iteratorRecord および environment）を実行し、その結果を返す。
- v を
undefined とする。 -
Assert : iteratorRecord.[[Done]] はfalse である。 -
next を
?
IteratorStepValue (iteratorRecord) とする。 -
next が
done でない場合、- v に next を設定する。
-
?
BindingInitialization ofBindingIdentifier （引数 v および environment）を実行し、その結果を返す。
8.6.4 静的セマンティクス: AssignmentTargetType
-
IsStrict (このIdentifierReference ) がtrue であり、かつStringValue ofIdentifier が"eval" または"arguments" のいずれかである場合、invalid を返す。 simple を返す。
simple を返す。
-
expr を
ParenthesizedExpression （CoverParenthesizedExpressionAndArrowParameterList によりcover されたもの）とする。 -
expr の
AssignmentTargetType を返す。
-
ホスト がウェブブラウザーであるか、または関数呼び出し代入ターゲットの実行時エラー をサポートしており、IsStrict (このCallExpression ) がfalse の場合、web-compat を返す。
invalid を返す。
invalid を返す。
8.6.5 静的セマンティクス: PropName
-
IdentifierReference のStringValue を返す。
empty を返す。
-
PropertyName のPropName を返す。
-
IdentifierName のStringValue を返す。
-
StringLiteral のSV を返す。
-
nbr を
NumericLiteral のNumericValue とする。 -
!
ToString (nbr) を返す。
empty を返す。
-
ClassElementName のPropName を返す。
-
ClassElementName のPropName を返す。
-
ClassElementName のPropName を返す。
empty を返す。
empty を返す。
-
ClassElementName のPropName を返す。
-
ClassElementName のPropName を返す。
empty を返す。
9 実行可能コードと実行コンテキスト
9.1 環境レコード
Environment Record
は、ECMAScriptコードの字句的なネスト構造に基づいて、
すべての Environment Record には [[OuterEnv]] フィールドがあり、これは
Environment Record は純粋に仕様上の仕組みであり、ECMAScript 実装の特定のアーティファクトに対応している必要はありません。ECMAScript プログラムがこれらの値に直接アクセスしたり操作することはできません。
9.1.1 環境レコード型の階層
-
-
宣言的環境レコード は、FunctionDeclaration 、VariableDeclaration 、Catch 節などの ECMAScript 言語構文要素の効果を、識別子バインディングをECMAScript 言語値 に直接関連付けることで定義するために使用されます。-
関数環境レコード は、ECMAScript の関数オブジェクト の呼び出しに対応し、その関数内のトップレベル宣言に対するバインディングを含みます。新しいthisバインディングを確立することができます。また、superメソッド呼び出しをサポートするために必要な状態も保持します。 -
モジュール環境レコード は、Module のトップレベル宣言のバインディングを持ちます。また、Module によって明示的にインポートされたバインディングも含まれます。その [[OuterEnv]] はグローバル環境レコード です。
-
-
オブジェクト環境レコード は、WithStatement のような ECMAScript の要素が、識別子バインディングをあるオブジェクトのプロパティに関連付ける効果を定義するために使用されます。 -
グローバル環境レコード は、Script のグローバル宣言のために使用されます。これは外側環境を持たず、その [[OuterEnv]] はnull です。識別子バインディングを事前に持つ場合があり、またグローバルオブジェクト が関連付けられており、そのプロパティがグローバル環境の識別子バインディングの一部を提供します。ECMAScript コードの実行により、グローバルオブジェクト に追加のプロパティが追加されたり、初期プロパティが変更されたりします。
-
| メソッド | 目的 |
|---|---|
| HasBinding(N) |
|
| CreateMutableBinding(N, D) |
|
| CreateImmutableBinding(N, S) |
|
| InitializeBinding(N, V) |
|
| SetMutableBinding(N, V, S) |
|
| GetBindingValue(N, S) |
|
| DeleteBinding(N) |
|
| HasThisBinding() |
this バインディングを確立するかどうか判定する。確立する場合は
|
| HasSuperBinding() |
super メソッドバインディングを確立するかどうか判定する。確立する場合は
|
| WithBaseObject() |
この with 文に関連付けられている場合は、その with オブジェクトを返す。それ以外の場合は
|
9.1.1.1 宣言的環境レコード
各宣言的環境レコードは、変数、定数、let、class、module、import、関数宣言を含むECMAScriptプログラムスコープに関連付けられています。宣言的環境レコードは、そのスコープ内に含まれる宣言によって定義された識別子の集合をバインドします。
9.1.1.1.1 HasBinding ( N )
- もし envRec が N のバインディングを持っていれば、
true を返す。 false を返す。
9.1.1.1.2 CreateMutableBinding ( N, D )
アサート : envRec は既に N のバインディングを持っていない。- envRec に N の可変バインディングを作成し、未初期化であることを記録する。D が
true なら、作成したバインディングが後続の DeleteBinding 呼び出しにより削除可能であることを記録する。 unused を返す。
9.1.1.1.3 CreateImmutableBinding ( N, S )
アサート : envRec は既に N のバインディングを持っていない。- envRec に N の不変バインディングを作成し、未初期化であることを記録する。S が
true なら、作成したバインディングが strict バインディングであることを記録する。 unused を返す。
9.1.1.1.4 InitializeBinding ( N, V )
アサート : envRec は N の未初期化バインディングを持っていること。- envRec の N のバインディング値を V に設定する。
記録 ：envRec の N のバインディングが初期化済みであることを記録する。unused を返す。
9.1.1.1.5 SetMutableBinding ( N, V, S )
-
もし envRec が N のバインディングを持たない場合、
- もし S が
true なら、ReferenceError 例外を投げる。 - ! envRec.CreateMutableBinding(N,
true ) を実行する。 - ! envRec.InitializeBinding(N, V) を実行する。
unused を返す。
- もし S が
- もし envRec の N のバインディングが strict バインディングなら、S を
true に設定する。 - もし envRec の N のバインディングが未初期化なら、
ReferenceError 例外を投げる。
- それ以外で、envRec の N のバインディングが可変バインディングなら、
- その値を V に変更する。
- それ以外、
アサート : これは不変バインディングの値を変更しようとしている。- もし S が
true なら、TypeError 例外を投げる。
unused を返す。
ステップ
function f() { eval("var x; x = (delete x, 0);"); }9.1.1.1.6 GetBindingValue ( N, S )
アサート : envRec は N のバインディングを持っている。- もし envRec の N のバインディングが未初期化なら
ReferenceError 例外を投げる。 - envRec の N に現在バインドされている値を返す。
9.1.1.1.7 DeleteBinding ( N )
アサート : envRec は N のバインディングを持っている。- もし envRec の N のバインディングが削除できない場合、
false を返す。 - envRec から N のバインディングを削除する。
true を返す。
9.1.1.1.8 HasThisBinding ( )
false を返す。
通常の this バインディングを提供しません。
9.1.1.1.9 HasSuperBinding ( )
false を返す。
通常の super バインディングを提供しません。
9.1.1.1.10 WithBaseObject ( )
undefined を返す。
9.1.1.2 オブジェクト環境レコード
各オブジェクト環境レコードは、自身のバインディングオブジェクトと呼ばれるオブジェクトに関連付けられています。オブジェクト環境レコードは、バインディングオブジェクトのプロパティ名と直接対応する文字列識別子名の集合をバインドします。
with文（
オブジェクト環境レコードは、
| フィールド名 | 値 | 意味 |
|---|---|---|
| [[BindingObject]] | オブジェクト |
この |
| [[IsWithEnvironment]] | ブール値 |
このwith文のために作成されたかどうかを示す。
|
9.1.1.2.1 HasBinding ( N )
- bindingObjectをenvRec.[[BindingObject]]とする。
- foundBindingを ?
HasProperty (bindingObject, N)とする。 - foundBindingが
false なら、false を返す。 - envRec.[[IsWithEnvironment]]が
false なら、true を返す。 - unscopablesを ?
Get (bindingObject,%Symbol.unscopables% )とする。 - unscopablesが
オブジェクト の場合、 true を返す。
9.1.1.2.2 CreateMutableBinding ( N, D )
- bindingObjectをenvRec.[[BindingObject]]とする。
- ?
DefinePropertyOrThrow (bindingObject, N, PropertyDescriptor { [[Value]]:undefined , [[Writable]]:true , [[Enumerable]]:true , [[Configurable]]: D })を実行する。 unused を返す。
通常envRecはNのバインディングを持っていませんが、持っている場合は、
9.1.1.2.3 CreateImmutableBinding ( N, S )
9.1.1.2.4 InitializeBinding ( N, V )
- ? envRec.SetMutableBinding(N,
V,
false )を実行する。 unused を返す。
本仕様では、
9.1.1.2.5 SetMutableBinding ( N, V, S )
- bindingObjectをenvRec.[[BindingObject]]とする。
- stillExistsを ?
HasProperty (bindingObject, N)とする。 - stillExistsが
false かつSがtrue なら、ReferenceError 例外を投げる。 - ?
Set (bindingObject, N, V, S)を実行する。 unused を返す。
9.1.1.2.6 GetBindingValue ( N, S )
- bindingObjectをenvRec.[[BindingObject]]とする。
- valueを ?
HasProperty (bindingObject, N)とする。 - valueが
false の場合、- Sが
false ならundefined を返し、そうでなければReferenceError 例外を投げる。
- Sが
- ?
Get (bindingObject, N)を返す。
9.1.1.2.7 DeleteBinding ( N )
- bindingObjectをenvRec.[[BindingObject]]とする。
- ? bindingObject.[[Delete]](N)を返す。
9.1.1.2.8 HasThisBinding ( )
false を返す。
thisバインディングを提供しません。
9.1.1.2.9 HasSuperBinding ( )
false を返す。
superバインディングを提供しません。
9.1.1.2.10 WithBaseObject ( )
- envRec.[[IsWithEnvironment]]が
true なら、envRec.[[BindingObject]]を返す。 - それ以外の場合、
undefined を返す。
9.1.1.3 関数環境レコード
関数環境レコードは、関数のトップレベルスコープを表すために使われるthisバインディングを提供します。関数がsuperを参照する場合、その関数環境レコードは関数内からsuperメソッド呼び出しを行うための状態も保持します。
関数環境レコードは
| フィールド名 | 値 | 意味 |
|---|---|---|
| [[ThisValue]] |
|
この関数呼び出しで使われる |
| [[ThisBindingStatus]] |
|
値が |
| [[FunctionObject]] |
ECMAScript |
この |
| [[NewTarget]] |
|
この |
関数環境レコードは、
9.1.1.3.1 BindThisValue ( envRec, V )
抽象操作 BindThisValue は、引数 envRec（
アサート : envRec.[[ThisBindingStatus]]はlexical でないこと。- envRec.[[ThisBindingStatus]]が
initialized なら、ReferenceError 例外を投げる。 - envRec.[[ThisValue]]にVを設定する。
- envRec.[[ThisBindingStatus]]に
initialized を設定する。 unused を返す。
9.1.1.3.2 HasThisBinding ( )
- envRec.[[ThisBindingStatus]]が
lexical ならfalse を返し、それ以外ならtrue を返す。
9.1.1.3.3 HasSuperBinding ( )
- envRec.[[ThisBindingStatus]]が
lexical ならfalse を返す。 - envRec.[[FunctionObject]].[[HomeObject]]が
undefined ならfalse を返し、それ以外ならtrue を返す。
9.1.1.3.4 GetThisBinding ( )
アサート : envRec.[[ThisBindingStatus]]はlexical でないこと。- envRec.[[ThisBindingStatus]]が
uninitialized なら、ReferenceError 例外を投げる。 - envRec.[[ThisValue]]を返す。
9.1.1.3.5 GetSuperBase ( envRec )
抽象操作 GetSuperBase は、引数 envRec（superプロパティアクセスの基底となるオブジェクトを返す。値が
9.1.1.4 グローバル環境レコード
グローバル環境レコードは、共通の
グローバル環境レコードは論理的には単一のレコードですが、
グローバル環境レコードは、
| フィールド名 | 値 | 意味 |
|---|---|---|
| [[ObjectRecord]] |
|
バインディングオブジェクトは |
| [[GlobalThisValue]] | オブジェクト |
グローバルスコープにおけるthisの値。 |
| [[DeclarativeRecord]] |
|
|
| メソッド | 目的 |
|---|---|
| GetThisBinding() |
このthisバインディングの値を返す。
|
9.1.1.4.1 HasBinding ( N )
- DclRecをenvRec.[[DeclarativeRecord]]とする。
- ! DclRec.HasBinding(N)が
true なら、true を返す。 - ObjRecをenvRec.[[ObjectRecord]]とする。
- ? ObjRec.HasBinding(N)を返す。
9.1.1.4.2 CreateMutableBinding ( N, D )
- DclRecをenvRec.[[DeclarativeRecord]]とする。
- ! DclRec.HasBinding(N)が
true なら、TypeError 例外を投げる。 - ! DclRec.CreateMutableBinding(N, D)を返す。
9.1.1.4.3 CreateImmutableBinding ( N, S )
- DclRecをenvRec.[[DeclarativeRecord]]とする。
- ! DclRec.HasBinding(N)が
true なら、TypeError 例外を投げる。 - ! DclRec.CreateImmutableBinding(N, S)を返す。
9.1.1.4.4 InitializeBinding ( N, V )
- DclRecをenvRec.[[DeclarativeRecord]]とする。
- ! DclRec.HasBinding(N)が
true なら、- ! DclRec.InitializeBinding(N, V)を返す。
アサート ：バインディングが存在する場合、それはオブジェクト環境レコード に存在しなければならない。- ObjRecをenvRec.[[ObjectRecord]]とする。
- ? ObjRec.InitializeBinding(N, V)を返す。
9.1.1.4.5 SetMutableBinding ( N, V, S )
- DclRecをenvRec.[[DeclarativeRecord]]とする。
- ! DclRec.HasBinding(N)が
true なら、- ? DclRec.SetMutableBinding(N, V, S)を返す。
- ObjRecをenvRec.[[ObjectRecord]]とする。
- ? ObjRec.SetMutableBinding(N, V, S)を返す。
9.1.1.4.6 GetBindingValue ( N, S )
- DclRecをenvRec.[[DeclarativeRecord]]とする。
- ! DclRec.HasBinding(N)が
true なら、- ? DclRec.GetBindingValue(N, S)を返す。
- ObjRecをenvRec.[[ObjectRecord]]とする。
- ? ObjRec.GetBindingValue(N, S)を返す。
9.1.1.4.7 DeleteBinding ( N )
- DclRecをenvRec.[[DeclarativeRecord]]とする。
- ! DclRec.HasBinding(N)が
true なら、- ! DclRec.DeleteBinding(N)を返す。
- ObjRecをenvRec.[[ObjectRecord]]とする。
- globalObjectをObjRec.[[BindingObject]]とする。
- existingPropを?
HasOwnProperty (globalObject, N)とする。 - existingPropが
true なら、- ? ObjRec.DeleteBinding(N)を返す。
true を返す。
9.1.1.4.8 HasThisBinding ( )
true を返す。
thisバインディングを提供します。
9.1.1.4.9 HasSuperBinding ( )
false を返す。
superバインディングを提供しません。
9.1.1.4.10 WithBaseObject ( )
undefined を返す。
9.1.1.4.11 GetThisBinding ( )
- envRec.[[GlobalThisValue]]を返す。
9.1.1.4.12 HasLexicalDeclaration ( envRec, N )
抽象操作 HasLexicalDeclaration は、引数envRec（
- DclRecをenvRec.[[DeclarativeRecord]]とする。
- ! DclRec.HasBinding(N)を返す。
9.1.1.4.13 HasRestrictedGlobalProperty ( envRec, N )
抽象操作 HasRestrictedGlobalProperty は、引数envRec（
- ObjRecをenvRec.[[ObjectRecord]]とする。
- globalObjectをObjRec.[[BindingObject]]とする。
- existingPropを? globalObject.[[GetOwnProperty]](N)とする。
- existingPropが
undefined なら、false を返す。 - existingProp.[[Configurable]]が
true なら、false を返す。 true を返す。
9.1.1.4.14 CanDeclareGlobalVar ( envRec, N )
抽象操作 CanDeclareGlobalVar は、引数 envRec（
- ObjRecをenvRec.[[ObjectRecord]]とする。
- globalObjectをObjRec.[[BindingObject]]とする。
- hasPropertyを?
HasOwnProperty (globalObject, N)とする。 - hasPropertyが
true なら、true を返す。 - ?
IsExtensible (globalObject)を返す。
9.1.1.4.15 CanDeclareGlobalFunction ( envRec, N )
抽象操作 CanDeclareGlobalFunction は、引数 envRec（
- ObjRecをenvRec.[[ObjectRecord]]とする。
- globalObjectをObjRec.[[BindingObject]]とする。
- existingPropを? globalObject.[[GetOwnProperty]](N)とする。
- existingPropが
undefined なら、?IsExtensible (globalObject)を返す。 - existingProp.[[Configurable]]が
true なら、true を返す。 IsDataDescriptor (existingProp)がtrue かつexistingPropの属性値が{ [[Writable]]:true , [[Enumerable]]:true }であれば、true を返す。false を返す。
9.1.1.4.16 CreateGlobalVarBinding ( envRec, N, D )
抽象操作 CreateGlobalVarBinding は、引数 envRec（
- ObjRecをenvRec.[[ObjectRecord]]とする。
- globalObjectをObjRec.[[BindingObject]]とする。
- hasPropertyを?
HasOwnProperty (globalObject, N)とする。 - extensibleを?
IsExtensible (globalObject)とする。 - hasPropertyが
false かつextensibleがtrue なら、- ? ObjRec.CreateMutableBinding(N, D)を実行する。
- ? ObjRec.InitializeBinding(N,
undefined )を実行する。
unused を返す。
9.1.1.4.17 CreateGlobalFunctionBinding ( envRec, N, V, D )
抽象操作 CreateGlobalFunctionBinding は、引数 envRec（
- ObjRecをenvRec.[[ObjectRecord]]とする。
- globalObjectをObjRec.[[BindingObject]]とする。
- existingPropを? globalObject.[[GetOwnProperty]](N)とする。
- existingPropが
undefined またはexistingProp.[[Configurable]]がtrue なら、- descをPropertyDescriptor { [[Value]]:
V, [[Writable]]:
true , [[Enumerable]]:true , [[Configurable]]: D }とする。
- descをPropertyDescriptor { [[Value]]:
V, [[Writable]]:
- それ以外の場合、
- descをPropertyDescriptor { [[Value]]: V }とする。
- ?
DefinePropertyOrThrow (globalObject, N, desc)を実行する。 - ?
Set (globalObject, N, V,false )を実行する。 unused を返す。
グローバル関数宣言は常に
9.1.1.5 モジュール環境レコード
モジュール環境レコードは、
モジュール環境レコードは、
| メソッド | 目的 |
|---|---|
| GetThisBinding() |
このthisバインディングの値を返す。
|
9.1.1.5.1 GetBindingValue ( N, S )
Sは常に
9.1.1.5.2 DeleteBinding ( N )
9.1.1.5.3 HasThisBinding ( )
true を返す。
thisバインディングを提供します。
9.1.1.5.4 GetThisBinding ( )
undefined を返す。
9.1.1.5.5 CreateImportBinding ( envRec, N, M, N2 )
抽象操作 CreateImportBinding は、引数 envRec（
9.1.2 環境レコードの操作
以下の
9.1.2.1 GetIdentifierReference ( env, name, strict )
抽象操作 GetIdentifierReference は、引数 env（
- envが
null なら、Reference Record { [[Base]]:unresolvable , [[ReferencedName]]: name, [[Strict]]: strict, [[ThisValue]]:empty } を返す。
- exists を ? env.HasBinding(name) とする。
- existsが
true なら、Reference Record { [[Base]]: env, [[ReferencedName]]: name, [[Strict]]: strict, [[ThisValue]]:empty } を返す。
- それ以外の場合、
- outer を env.[[OuterEnv]] とする。
- ?
GetIdentifierReference (outer, name, strict) を返す。
9.1.2.2 NewDeclarativeEnvironment ( E )
抽象操作 NewDeclarativeEnvironment は、引数 E（
- env をバインディングが何もない新しい
宣言的環境レコード とする。 - env.[[OuterEnv]] に E を設定する。
- env を返す。
9.1.2.3 NewObjectEnvironment ( O, W, E )
抽象操作 NewObjectEnvironment は、引数 O（オブジェクト）、W（ブール値）、E（
- env を新しい
オブジェクト環境レコード とする。 - env.[[BindingObject]] に O を設定する。
- env.[[IsWithEnvironment]] に W を設定する。
- env.[[OuterEnv]] に E を設定する。
- env を返す。
9.1.2.4 NewFunctionEnvironment ( F, newTarget )
抽象操作 NewFunctionEnvironment は、引数 F（ECMAScript
- env をバインディングが何もない新しい
関数環境レコード とする。 - env.[[FunctionObject]] に F を設定する。
- F.[[ThisMode]] が
lexical なら、env.[[ThisBindingStatus]] にlexical を設定する。 - それ以外の場合、env.[[ThisBindingStatus]] に
uninitialized を設定する。 - env.[[NewTarget]] に newTarget を設定する。
- env.[[OuterEnv]] に F.[[Environment]] を設定する。
- env を返す。
9.1.2.5 NewGlobalEnvironment ( G, thisValue )
抽象操作 NewGlobalEnvironment は、引数 G（オブジェクト）、thisValue（オブジェクト）を取り、
- objRec を
NewObjectEnvironment (G,false ,null ) とする。 - dclRec を
NewDeclarativeEnvironment (null ) とする。 - env を新しい
グローバル環境レコード とする。 - env.[[ObjectRecord]] に objRec を設定する。
- env.[[GlobalThisValue]] に thisValue を設定する。
- env.[[DeclarativeRecord]] に dclRec を設定する。
- env.[[OuterEnv]] に
null を設定する。 - env を返す。
9.1.2.6 NewModuleEnvironment ( E )
抽象操作 NewModuleEnvironment は、引数 E（
- env をバインディングが何もない新しい
モジュール環境レコード とする。 - env.[[OuterEnv]] に E を設定する。
- env を返す。
9.2 プライベート環境レコード
プライベート環境レコードは、ECMAScriptコード内の
各
| フィールド名 | 値の型 | 意味 |
|---|---|---|
| [[OuterPrivateEnvironment]] |
|
最も近い外側のクラスの |
| [[Names]] |
|
このクラスによって宣言された |
9.2.1 プライベート環境レコードの操作
以下の
9.2.1.1 NewPrivateEnvironment ( outerPrivateEnv )
抽象操作 NewPrivateEnvironment は、引数 outerPrivateEnv（
- names を新しい空の
リスト とする。 -
プライベート環境レコード { [[OuterPrivateEnvironment]]: outerPrivateEnv, [[Names]]: names } を返す。
9.2.1.2 ResolvePrivateIdentifier ( privateEnv, identifier )
抽象操作 ResolvePrivateIdentifier は、引数 privateEnv（
- names を privateEnv.[[Names]] とする。
-
names の各
プライベート名 pnについて、- pn.[[Description]] が
identifier であれば、
- pn を返す。
- pn.[[Description]] が
identifier であれば、
- outerPrivateEnv を privateEnv.[[OuterPrivateEnvironment]] とする。
アサート ：outerPrivateEnvはnull ではない。-
ResolvePrivateIdentifier (outerPrivateEnv, identifier) を返す。
9.3 レルム
評価される前に、すべてのECMAScriptコードはレルムに関連付けられていなければなりません。概念的には、
| フィールド名 | 値 | 意味 |
|---|---|---|
| [[AgentSignifier]] |
|
この |
| [[Intrinsics]] |
|
この |
| [[GlobalObject]] | オブジェクト |
この |
| [[GlobalEnv]] |
|
この |
| [[TemplateMap]] |
|
テンプレートオブジェクトは各 ある
|
| [[LoadedModules]] |
|
この import()式が |
| [[HostDefined]] |
任意（デフォルト値は |
|
9.3.1 InitializeHostDefinedRealm ( )
抽象操作 InitializeHostDefinedRealm は引数を取らず、
- realm を新しい
レルムレコード とする。 CreateIntrinsics (realm)を実行する。- realm.[[AgentSignifier]]に
AgentSignifier ()の値を設定する。 - realm.[[TemplateMap]]に新しい空の
リスト を設定する。 - newContext を新しい
実行コンテキスト とする。 - newContextのFunctionを
null に設定する。 - newContextの
レルム をrealmに設定する。 - newContextのScriptOrModuleを
null に設定する。 - newContextを
実行コンテキストスタック にプッシュする。newContextが実行中の実行コンテキスト となる。 ホスト がエキゾチックオブジェクト をrealmのグローバルオブジェクト として必要とする場合、- globalをそのようなオブジェクトとして
ホスト定義 の方法で作成する。
- globalをそのようなオブジェクトとして
- それ以外の場合、
- globalを
OrdinaryObjectCreate (realm.[[Intrinsics]].[[%Object.prototype% ]])とする。
- globalを
ホスト がrealmのグローバルスコープのthisバインディングをグローバルオブジェクト 以外のオブジェクトにする必要がある場合、- thisValueをそのようなオブジェクトとして
ホスト定義 の方法で作成する。
- thisValueをそのようなオブジェクトとして
- それ以外の場合、
- thisValueをglobalとする。
- realm.[[GlobalObject]]にglobalを設定する。
- realm.[[GlobalEnv]]に
NewGlobalEnvironment (global, thisValue)を設定する。 - ?
SetDefaultGlobalBindings (realm)を実行する。 ホスト定義 のグローバルオブジェクト プロパティをglobalに作成する。unused を返す。
9.3.2 CreateIntrinsics ( realmRec )
抽象操作 CreateIntrinsics は、引数 realmRec（
- realmRec.[[Intrinsics]] に新しい
レコード を設定する。 - realmRec.[[Intrinsics]]のフィールドに、
表6 に記載の値を設定する。フィールド名は表の第1列。値は、この仕様の19 から28 各オブジェクトの仕様に従って完全かつ再帰的にプロパティ値が設定された新しいオブジェクト値。すべてのオブジェクトプロパティ値は新しいオブジェクト値。組み込み関数オブジェクト はCreateBuiltinFunction (steps, length, name, slots, realmRec, prototype) で作成される。stepsはこの仕様で定義された関数、nameは関数の"name" プロパティの初期値、lengthは"length" プロパティの初期値、slotsは内部スロット名リスト、prototypeは[[Prototype]]内部スロットの指定値。組み込みとそのプロパティの作成順序は、未作成のオブジェクトへの依存が発生しないようにしなければならない。 AddRestrictedFunctionProperties (realmRec.[[Intrinsics]].[[%Function.prototype% ]], realmRec)を実行する。unused を返す。
9.3.3 SetDefaultGlobalBindings ( realmRec )
抽象操作 SetDefaultGlobalBindings は、引数 realmRec（
- globalをrealmRec.[[GlobalObject]]とする。
19 で指定されるグローバルオブジェクトの各プロパティについて、- nameを
プロパティ名 の文字列値とする。 - descを、そのプロパティの指定属性を含む完全なデータ
プロパティディスクリプタ とする。19.2 、19.3 、19.4 に列挙されるプロパティの場合、[[Value]]属性の値はrealmRecの対応する組み込みオブジェクト。 - ?
DefinePropertyOrThrow (global, name, desc)を実行する。
- nameを
unused を返す。
9.4 実行コンテキスト
実行コンテキストは、ECMAScriptの実装によるコードの実行時評価を追跡するために使用される仕様デバイスです。任意の時点で、実際にコードを実行している
実行コンテキストスタックは、実行コンテキストを追跡するために使用されます。
実行コンテキストは、それに関連付けられたコードの実行進捗を追跡するために必要な実装依存の状態を含みます。各実行コンテキストは、少なくとも
| コンポーネント | 目的 |
|---|---|
| code evaluation state |
この |
| Function |
もしこの |
|
|
関連コードがECMAScriptリソースへアクセスするために利用する |
| ScriptOrModule |
関連コードが由来する |
ECMAScriptコード実行コンテキストは、
| コンポーネント | 目的 |
|---|---|
| LexicalEnvironment |
この |
| VariableEnvironment |
この |
| PrivateEnvironment |
直近の包含クラス内で |
実行コンテキストのLexicalEnvironmentおよびVariableEnvironmentコンポーネントは常に
ジェネレーターの評価を表す実行コンテキストは、
| コンポーネント | 目的 |
|---|---|
| Generator |
この |
ほとんどの場合、仕様内のアルゴリズムによって直接操作されるのは
実行コンテキストは純粋に仕様上の仕組みであり、ECMAScript実装の特定の構造体に対応している必要はありません。ECMAScriptコードから直接実行コンテキストにアクセスしたり観察したりすることはできません。
9.4.1 GetActiveScriptOrModule ( )
抽象操作GetActiveScriptOrModuleは引数を取らず、
- もし
実行コンテキストスタック が空であれば、null を返す。 - ecを、
実行コンテキストスタック 上のScriptOrModuleコンポーネントがnull でない最上位の実行コンテキスト とする。 - そのような
実行コンテキスト が存在しない場合、null を返す。そうでなければ、ecのScriptOrModuleを返す。
9.4.2 ResolveBinding ( name [ , env ] )
抽象操作ResolveBindingは、引数name（文字列）および省略可能な引数env（
- もしenvが指定されていない、またはenvが
undefined の場合、- envに
実行中の実行コンテキスト のLexicalEnvironmentを設定する。
- envに
保証 ：envはEnvironment Record である。- strictを
IsStrict (評価中の構文生成規則)とする。 - 戻り値は?
GetIdentifierReference (env, name, strict)とする。
ResolveBindingの結果は常に、その[[ReferencedName]]フィールドがnameとなる
9.4.3 GetThisEnvironment ( )
抽象操作GetThisEnvironmentは引数を取らず、thisのバインディングを提供する
- envを
実行中の実行コンテキスト のLexicalEnvironmentとする。 - 繰り返す。
- existsをenv.HasThisBinding()とする。
- もしexistsが
true なら、envを返す。 - outerをenv.[[OuterEnv]]とする。
保証 ：outerはnull でない。- envにouterを設定する。
ステップthisバインディングを持つグローバル環境で終わるからです。
9.4.4 ResolveThisBinding ( )
抽象操作ResolveThisBindingは引数を取らず、thisのバインディングを決定します。呼び出し時、次の手順を実行します:
- envRecを
GetThisEnvironment ()とする。 - 戻り値は? envRec.GetThisBinding()とする。
9.4.5 GetNewTarget ( )
抽象操作GetNewTargetは引数を取らず、オブジェクトまたは
- envRecを
GetThisEnvironment ()とする。 保証 ：envRecは[[NewTarget]]フィールドを持つ。- 戻り値はenvRec.[[NewTarget]]とする。
9.4.6 GetGlobalObject ( )
抽象操作GetGlobalObjectは引数を取らず、オブジェクトを返します。これは、現在の
- currentRealmを
現在のRealm Record とする。 - 戻り値はcurrentRealm.[[GlobalObject]]とする。
9.5 ジョブおよびジョブをキューに入れるためのホスト操作
ジョブとは、パラメータを持たず、他のECMAScript計算が現在進行中でないときにECMAScript計算を開始する
- ジョブがスケジュールされた
エージェント において、実行中のコンテキストがなく、そのエージェント の実行コンテキストスタック が空である将来のある時点で、実装は以下を行う必要があります:- 任意の
ホスト定義 の準備ステップを実行する。 呼び出す ジョブ となる抽象クロージャ 。- 任意の
ホスト定義 のクリーンアップステップを実行し、その後実行コンテキストスタック が空であることを保証する。
- 任意の
- 任意の時点で、1つの
エージェント 内で同時に評価中のジョブ は1つだけでなければなりません。 - 一度ある
ジョブ の評価が開始されたら、その評価は同じエージェント 内で他のジョブ の評価が始まる前に完了しなければなりません。 抽象クロージャ はnormal completion を返さなければならず、エラーの処理は自ら実装しなければなりません。
ある時点で、すべての次の条件が真であれば、scriptOrModule（
GetActiveScriptOrModule ()がscriptOrModuleである。- もしscriptOrModuleが
Script Record またはModule Record なら、ecを実行コンテキストスタック 上でScriptOrModuleコンポーネントがscriptOrModuleである最上位の実行コンテキスト とし、ecのRealm コンポーネントはscriptOrModule.[[Realm]]である。
ある時点で、すべての次の条件が真であれば、実行はECMAScriptコードを評価する準備ができている状態です:
実行コンテキストスタック が空でない。実行コンテキストスタック 上の最上位の実行コンテキスト のRealm コンポーネントがRealm Record である。
特定の種類の
9.5.1 JobCallbackレコード
JobCallbackレコードは、
WHATWG HTML仕様（https://html.spec.whatwg.org/）は、例えばPromiseコールバックのためにインカンバント設定オブジェクトを伝播するために
JobCallbackレコードは、
| フィールド名 | 値 | 意味 |
|---|---|---|
| [[Callback]] |
|
|
| [[HostDefined]] |
任意の値（デフォルト値は |
|
9.5.2 HostMakeJobCallback ( callback )
HostMakeJobCallbackの実装は、以下の要件を満たさなければなりません：
- [[Callback]]フィールドがcallbackである
JobCallbackレコード を返さなければなりません。
HostMakeJobCallbackのデフォルト実装は、呼び出し時に次の手順を実行します：
JobCallbackレコード { [[Callback]]: callback, [[HostDefined]]:empty }を返す。
WebブラウザでないECMAScript
これは、コールバックが最終的にスケジュールされ実行される責任を持つ関数に渡された時点で呼び出されます。たとえば、promise.then(thenAction)はPromise.prototype.thenの呼び出し時にthenActionに対してMakeJobCallbackを呼び出しますが、リアクション
9.5.3 HostCallJobCallback ( jobCallback, V, argumentsList )
HostCallJobCallbackの実装は、以下の要件を満たさなければなりません：
Call (jobCallback.[[Callback]], V, argumentsList)を実行し、その結果を返さなければなりません。
HostCallJobCallbackのデフォルト実装は、呼び出し時に次の手順を実行します：
保証 :IsCallable (jobCallback.[[Callback]])はtrue である。- ?
Call (jobCallback.[[Callback]], V, argumentsList)を返す。
WebブラウザでないECMAScript
9.5.4 HostEnqueueGenericJob ( job, realm )
HostEnqueueGenericJobの実装は、
9.5.5 HostEnqueuePromiseJob ( job, realm )
HostEnqueuePromiseJobの実装は、
- もしrealmが
null でない場合、jobが呼び出されるたびに、実装はその呼び出し時に実行がECMAScriptコードを評価する準備ができている 状態であることを保証する実装依存 のステップを実行しなければなりません。 - HostEnqueuePromiseJobが呼び出された時点で
GetActiveScriptOrModule ()の値をscriptOrModuleとする。もしrealmがnull でない場合、毎回jobが呼び出されるたびに、実装はscriptOrModuleがその呼び出し時にアクティブなスクリプトまたはモジュール であることを保証する実装依存 のステップを実行しなければなりません。 ジョブ は、それらをスケジュールしたHostEnqueuePromiseJob呼び出しの順番と同じ順序で実行されなければなりません。
9.5.6 HostEnqueueTimeoutJob ( timeoutJob, realm, milliseconds )
HostEnqueueTimeoutJobの実装は、
9.6 エージェント
エージェントは、一連のECMAScript
例えば、一部のウェブブラウザーは、複数の無関係なタブ間で一つの
エージェント識別子は、
| フィールド名 | 値 | 意味 |
|---|---|---|
| [[LittleEndian]] | Boolean | |
| [[CanBlock]] | Boolean | |
| [[Signifier]] | 自身の |
|
| [[IsLockFree1]] | Boolean | 1 |
| [[IsLockFree2]] | Boolean | 2 |
| [[IsLockFree8]] | Boolean | 8 |
| [[CandidateExecution]] | ||
| [[KeptAlive]] | 新たな空 |
|
| [[ModuleAsyncEvaluationCount]] | 初期値0。非同期もしくは非同期依存を持つモジュールの[[AsyncEvaluationOrder]]フィールドに一意な増加値を割り当てるために使用。 |
[[Signifier]]、[[IsLockFree1]]、[[IsLockFree2]]の値は、一度
[[IsLockFree1]]および[[IsLockFree2]]の値は、必ずしもハードウェアによって決まるものではなく、実装ごと・時間ごとに異なる実装選択を反映することがあります。
[[IsLockFree4]]フィールドは存在しません。4バイトのアトミック操作は常にロックフリーです。
実際には、アトミック操作が何らかのロックを伴って実装されている場合、その操作はロックフリーではありません。ロックフリーはウェイトフリーを意味せず、ロックフリーなアトミック操作を完了するのに必要なマシンステップ数に上限はありません。
サイズnのアトミックアクセスがロックフリーであることは、サイズnの非アトミックアクセスの（見かけ上の）アトミシティについては何も意味しません。具体的には、非アトミックアクセスは複数の個別なメモリアクセスの連続として実行されることがあります。詳細は
9.6.1 AgentSignifier ( )
抽象操作AgentSignifierは引数を取らず、
- ARを
周囲のエージェント のエージェントレコード とする。 - AR.[[Signifier]]を返す。
9.6.2 AgentCanSuspend ( )
抽象操作AgentCanSuspendは引数を取らず、Booleanを返します。呼び出し時、次の手順を実行します：
- ARを
周囲のエージェント のエージェントレコード とする。 - AR.[[CanBlock]]を返す。
環境によっては、特定の
9.6.3 IncrementModuleAsyncEvaluationCount ( )
抽象操作IncrementModuleAsyncEvaluationCountは引数を取らず、
- ARを
周囲のエージェント のエージェントレコード とする。 - countをAR.[[ModuleAsyncEvaluationCount]]とする。
- AR.[[ModuleAsyncEvaluationCount]]にcount+1を設定する。
- countを返す。
この値は未処理モジュール間の相対評価順序を追跡するためだけに使用されます。未処理モジュールが存在しない場合、実装は[[ModuleAsyncEvaluationCount]]を密かに0にリセットしてもかまいません。
9.7 エージェントクラスタ
エージェントクラスタは、共有メモリ上で操作することで通信できる
すべての
クラスタ内のすべての
同一エージェントクラスタ内で異なる
クラスタ内のすべての
クラスタ内のすべての
埋め込み環境は、
この制約は、他の
この制約の帰結として、埋め込み環境内で同じサスペンド／ウェイク集団に属さない
埋め込み環境は、クラスタ内の他の
以下の仕様値およびそれらから伝播的に到達可能な値は、正確に1つのエージェントクラスタに属します。
クラスタ内のいずれかの
同じエージェントクラスタ内のすべての
エージェントクラスタは仕様上の仕組みであり、ECMAScript実装の特定の構造物に対応している必要はありません。
9.8 フォワードプログレス
実装は以下を保証しなければなりません：
- 専用の
実行スレッド を持つ、すべてのアンブロックされたエージェント が最終的にフォワードプログレスを行うこと 実行スレッド を共有するエージェント の集合において、いずれか1つのエージェント が最終的にフォワードプログレスを行うこと- ある
エージェント が、ブロッキングを提供する明示的なAPI以外の手段で他のエージェント をブロック状態にしないこと
9.9 WeakRefおよびFinalizationRegistryターゲットの処理モデル
9.9.1 目標
本仕様は、いかなるオブジェクトやシンボルもガベージコレクションされることを保証しません。
-
WeakRef.prototype.derefが呼ばれたとき、（undefined が返されない場合）参照先は生存し続け、以降の同期的なアクセスでも同じ値が返されます。このリストは、同期的な作業がClearKeptObjects 抽象操作によって終了したときにリセットされます。 -
FinalizationRegistry に登録されたオブジェクトやシンボルが到達不能になった場合、同期的なECMAScript実行が完了した後、FinalizationRegistry のクリーンアップコールバックの呼び出しが最終的に行われることがあります。クリーンアップはCleanupFinalizationRegistry 抽象操作で実行されます。
これらのアクション（
一部のECMAScript実装には、ECMAScriptがアイドル状態のときも含めてバックグラウンドで動作するガベージコレクタの実装が含まれています。
9.9.2 ライブネス
あるオブジェクトやシンボルの集合Sについて、仮想的なWeakRef非考慮実行とは、Sの要素を参照する
評価中の任意の時点で、オブジェクトやシンボルの集合Sは、次のいずれかの条件を満たす場合にライブと見なされます：
フィールド、内部スロット、またはプロパティにオブジェクトやシンボルが存在することは、その値がライブであることを意味しません。たとえば、その値がプログラムに返されない場合は観測できません。
これはWeakMapのキーやWeakSetのメンバー、
上記定義は、WeakMapのキーがライブでない場合、その対応する値も必ずしもライブでないことを意味します。
9.9.3 実行
任意の時点で、オブジェクトやシンボルの集合Sが
- Sの各要素valueについて、次を行う
- ref.[[WeakRefTarget]]がvalueである
WeakRef refそれぞれについて、次を行う- ref.[[WeakRefTarget]]を
empty に設定する。
- ref.[[WeakRefTarget]]を
- fg.[[Cells]]に、cell.[[WeakRefTarget]]がvalueである
Record cellを含むFinalizationRegistry fgそれぞれについて、次を行う- cell.[[WeakRefTarget]]を
empty に設定する。 - 必要に応じて
HostEnqueueFinalizationRegistryCleanupJob (fg)を実行する。
- cell.[[WeakRefTarget]]を
- map.[[WeakMapData]]に、r.[[Key]]がvalueである
Record rを含むWeakMap mapそれぞれについて、次を行う- r.[[Key]]を
empty に設定する。 - r.[[Value]]を
empty に設定する。
- r.[[Key]]を
- set.[[WeakSetData]]にvalueを含むWeakSet
setそれぞれについて、次を行う
- set.[[WeakSetData]]内の値がvalueである要素を、値が
empty である要素に置き換える。
- set.[[WeakSetData]]内の値がvalueである要素を、値が
- ref.[[WeakRefTarget]]がvalueである
ライブネスの定義と合わせて、この節は
オブジェクトの識別性を観測せずにアクセスすることは可能です。逃避しないオブジェクトのプロパティへのスカラ置換やデッドバリアブル除去など、識別性が観測されない場合の最適化は許されます。従って、そのようなオブジェクトを指す
一方、オブジェクトの識別性が観測され、そのオブジェクトが
9.9.4 ホストフック
9.9.4.1 HostEnqueueFinalizationRegistryCleanupJob ( finalizationRegistry )
cleanupJobを、引数を取らずfinalizationRegistryをキャプチャし、呼び出されたときに次の手順を実行する新たな
- cleanupResultを
Completion (CleanupFinalizationRegistry (finalizationRegistry))とする。 - もしcleanupResultが
abrupt completion であれば、エラー報告のためのホスト定義 の手順を実行する。 unused を返す。
HostEnqueueFinalizationRegistryCleanupJobの実装は、可能であればcleanupJobを将来のある時点で実行されるようスケジューリングします。また、
9.10 ClearKeptObjects ( )
抽象操作ClearKeptObjectsは引数を取らず、
- agentRecordを
周囲のエージェント のエージェントレコード とする。 - agentRecord.[[KeptAlive]]を新たな空の
List に設定する。 unused を返す。
9.11 AddToKeptObjects ( value )
抽象操作AddToKeptObjectsは引数value（オブジェクトまたはシンボル）を取り、
- agentRecordを
周囲のエージェント のエージェントレコード とする。 - valueをagentRecord.[[KeptAlive]]に追加する。
unused を返す。
9.12 CleanupFinalizationRegistry ( finalizationRegistry )
抽象操作CleanupFinalizationRegistryは引数finalizationRegistry（
保証 ：finalizationRegistryは[[Cells]]および[[CleanupCallback]]内部スロットを持つ。- callbackをfinalizationRegistry.[[CleanupCallback]]とする。
- finalizationRegistry.[[Cells]]に、cell.[[WeakRefTarget]]が
empty であるRecord cellが含まれている間、実装は次の手順を実行してもよい：- そのようなcellを任意に選択する。
- cellをfinalizationRegistry.[[Cells]]から削除する。
- ?
HostCallJobCallback (callback,undefined , « cell.[[HeldValue]] » ) を実行する。
unused を返す。
9.13 CanBeHeldWeakly ( v )
抽象操作CanBeHeldWeaklyは引数v（
- もしvが
オブジェクトである なら、true を返す。 - もしvが
シンボルである かつKeyForSymbol (v)がundefined であるなら、true を返す。 false を返す。
10 通常オブジェクトおよびエキゾチックオブジェクトの挙動
10.1 通常オブジェクトの内部メソッドと内部スロット
すべての
すべての
以下のアルゴリズム記述では、Oは
各
10.1.1 [[GetPrototypeOf]] ( )
OrdinaryGetPrototypeOf (O)を返す。
10.1.1.1 OrdinaryGetPrototypeOf ( O )
抽象操作OrdinaryGetPrototypeOfは引数O（オブジェクト）を取り、オブジェクトまたは
- O.[[Prototype]]を返す。
10.1.2 [[SetPrototypeOf]] ( V )
OrdinarySetPrototypeOf (O, V)を返す。
10.1.2.1 OrdinarySetPrototypeOf ( O, V )
抽象操作OrdinarySetPrototypeOfは引数O（オブジェクト）、V（オブジェクトまたは
- currentをO.[[Prototype]]とする。
SameValue (V, current)がtrue なら、true を返す。- extensibleをO.[[Extensible]]とする。
- extensibleが
false なら、false を返す。 - pをVとする。
- doneを
false とする。 -
繰り返し、doneが
false の間、 - O.[[Prototype]]にVを設定する。
true を返す。
10.1.3 [[IsExtensible]] ( )
OrdinaryIsExtensible (O)を返す。
10.1.3.1 OrdinaryIsExtensible ( O )
抽象操作OrdinaryIsExtensibleは引数O（オブジェクト）を取り、Booleanを返します。呼び出されたとき、次の手順を実行します：
- O.[[Extensible]]を返す。
10.1.4 [[PreventExtensions]] ( )
OrdinaryPreventExtensions (O)を返す。
10.1.4.1 OrdinaryPreventExtensions ( O )
抽象操作OrdinaryPreventExtensionsは引数O（オブジェクト）を取り、
- O.[[Extensible]]に
false を設定する。 true を返す。
10.1.5 [[GetOwnProperty]] ( P )
OrdinaryGetOwnProperty (O, P)を返す。
10.1.5.1 OrdinaryGetOwnProperty ( O, P )
抽象操作OrdinaryGetOwnPropertyは引数O（オブジェクト）、P（
- OがキーPの独自プロパティを持たない場合、
undefined を返す。 - Dを新たなフィールドを持たない
プロパティディスクリプタ として作成する。 - XをキーPを持つOの独自プロパティとする。
- Xが
データプロパティ であれば、- D.[[Value]]にXの[[Value]]属性の値を設定する。
- D.[[Writable]]にXの[[Writable]]属性の値を設定する。
- そうでなければ、
- D.[[Enumerable]]にXの[[Enumerable]]属性の値を設定する。
- D.[[Configurable]]にXの[[Configurable]]属性の値を設定する。
- Dを返す。
10.1.6 [[DefineOwnProperty]] ( P, Desc )
- ?
OrdinaryDefineOwnProperty (O, P, Desc)を返す。
10.1.6.1 OrdinaryDefineOwnProperty ( O, P, Desc )
抽象操作OrdinaryDefineOwnPropertyは引数O（オブジェクト）、P（
- currentを? O.[[GetOwnProperty]](P)とする。
- extensibleを?
IsExtensible (O)とする。 ValidateAndApplyPropertyDescriptor (O, P, extensible, Desc, current)を返す。
10.1.6.2 IsCompatiblePropertyDescriptor ( Extensible, Desc, Current )
抽象操作IsCompatiblePropertyDescriptorは引数Extensible（Boolean）、Desc（
ValidateAndApplyPropertyDescriptor (undefined ,"" , Extensible, Desc, Current)を返す。
10.1.6.3 ValidateAndApplyPropertyDescriptor ( O, P, extensible, Desc, current )
抽象操作ValidateAndApplyPropertyDescriptorは、引数O（オブジェクトまたは
保証 ：Pはプロパティキー である。- もしcurrentが
undefined なら、- もしextensibleが
false なら、false を返す。 - もしOが
undefined なら、true を返す。 - もし
IsAccessorDescriptor (Desc)がtrue なら、 - それ以外の場合、
true を返す。
- もしextensibleが
保証 ：currentは全てのフィールドが埋められたプロパティディスクリプタ である。- もしDescがいかなるフィールドも持たないなら、
true を返す。 - もしcurrent.[[Configurable]]が
false なら、- もしDescが[[Configurable]]フィールドを持ち、かつDesc.[[Configurable]]が
true なら、false を返す。 - もしDescが[[Enumerable]]フィールドを持ち、かつDesc.[[Enumerable]]がcurrent.[[Enumerable]]と異なるなら、
false を返す。 - もし
IsGenericDescriptor (Desc)がfalse かつIsAccessorDescriptor (Desc)がIsAccessorDescriptor (current)と異なるなら、false を返す。 - もし
IsAccessorDescriptor (current)がtrue なら、 - それ以外の場合、もしcurrent.[[Writable]]が
false なら、
- もしDescが[[Configurable]]フィールドを持ち、かつDesc.[[Configurable]]が
- もしOが
undefined でないなら、- もし
IsDataDescriptor (current)がtrue かつIsAccessorDescriptor (Desc)がtrue なら、- もしDescが[[Configurable]]フィールドを持つならconfigurableをDesc.[[Configurable]]とし、なければcurrent.[[Configurable]]とする。
- もしDescが[[Enumerable]]フィールドを持つならenumerableをDesc.[[Enumerable]]とし、なければcurrent.[[Enumerable]]とする。
- オブジェクトOのPという名前のプロパティを、[[Configurable]]属性および[[Enumerable]]属性をそれぞれconfigurableおよびenumerableに、[[Get]]および[[Set]]属性をDescにそのフィールドがあればその値、なければ属性の
デフォルト値 に設定したアクセサプロパティ で置き換える。
- それ以外で、
IsAccessorDescriptor (current)がtrue かつIsDataDescriptor (Desc)がtrue なら、- もしDescが[[Configurable]]フィールドを持つならconfigurableをDesc.[[Configurable]]とし、なければcurrent.[[Configurable]]とする。
- もしDescが[[Enumerable]]フィールドを持つならenumerableをDesc.[[Enumerable]]とし、なければcurrent.[[Enumerable]]とする。
- オブジェクトOのPという名前のプロパティを、[[Configurable]]属性および[[Enumerable]]属性をそれぞれconfigurableおよびenumerableに、[[Value]]および[[Writable]]属性をDescにそのフィールドがあればその値、なければ属性の
デフォルト値 に設定したデータプロパティ で置き換える。
- それ以外の場合、
- Descの各フィールドについて、オブジェクトOのPという名前のプロパティの対応する属性にその値を設定する。
- もし
true を返す。
10.1.7 [[HasProperty]] ( P )
- Return ?
OrdinaryHasProperty (O, P).
10.1.7.1 OrdinaryHasProperty ( O, P )
抽象操作 OrdinaryHasProperty は、引数 O（オブジェクト）と P（
- hasOwn を ? O.[[GetOwnProperty]](P) とする。
- もし hasOwn が
undefined でなければ、true を返す。 - parent を ? O.[[GetPrototypeOf]]() とする。
- もし parent が
null でなければ、- Return ? parent.[[HasProperty]](P)。
false を返す。
10.1.8 [[Get]] ( P, Receiver )
- Return ?
OrdinaryGet (O, P, Receiver).
10.1.8.1 OrdinaryGet ( O, P, Receiver )
抽象操作 OrdinaryGet は、引数 O（オブジェクト）、P（
- desc を ? O.[[GetOwnProperty]](P) とする。
- もし desc が
undefined なら、- parent を ? O.[[GetPrototypeOf]]() とする。
- もし parent が
null なら、undefined を返す。 - Return ? parent.[[Get]](P, Receiver)。
- もし
IsDataDescriptor (desc) がtrue なら、desc.[[Value]] を返す。 保証 ：IsAccessorDescriptor (desc) がtrue である。- getter を desc.[[Get]] とする。
- もし getter が
undefined なら、undefined を返す。 - Return ?
Call (getter, Receiver)。
10.1.9 [[Set]] ( P, V, Receiver )
- Return ?
OrdinarySet (O, P, V, Receiver).
10.1.9.1 OrdinarySet ( O, P, V, Receiver )
抽象操作 OrdinarySet は、引数 O（オブジェクト）、P（
- ownDesc を ? O.[[GetOwnProperty]](P) とする。
- Return ?
OrdinarySetWithOwnDescriptor (O, P, V, Receiver, ownDesc)。
10.1.9.2 OrdinarySetWithOwnDescriptor ( O, P, V, Receiver, ownDesc )
抽象操作 OrdinarySetWithOwnDescriptor は、引数 O（オブジェクト）、P（
- もし ownDesc が
undefined なら、- parent を ? O.[[GetPrototypeOf]]() とする。
- もし parent が
null でなければ、- Return ? parent.[[Set]](P, V, Receiver)。
- それ以外の場合、
- ownDesc を PropertyDescriptor { [[Value]]:
undefined , [[Writable]]:true , [[Enumerable]]:true , [[Configurable]]:true } とする。
- ownDesc を PropertyDescriptor { [[Value]]:
- もし
IsDataDescriptor (ownDesc) がtrue なら、- もし ownDesc.[[Writable]] が
false なら、false を返す。 - もし Receiver
がオブジェクトでない なら、false を返す。 - existingDescriptor を ? Receiver.[[GetOwnProperty]](P) とする。
- もし existingDescriptor が
undefined でなければ、- もし
IsAccessorDescriptor (existingDescriptor) がtrue なら、false を返す。 - もし existingDescriptor.[[Writable]] が
false なら、false を返す。 - valueDesc を PropertyDescriptor { [[Value]]: V } とする。
- Return ? Receiver.[[DefineOwnProperty]](P, valueDesc)。
- もし
- それ以外の場合、
保証 ：Receiverは現在プロパティPを持たない。- Return ?
CreateDataProperty (Receiver, P, V)。
- もし ownDesc.[[Writable]] が
保証 ：IsAccessorDescriptor (ownDesc) がtrue である。- setter を ownDesc.[[Set]] とする。
- もし setter が
undefined なら、false を返す。 - ?
Call (setter, Receiver, « V ») を実行する。 true を返す。
10.1.10 [[Delete]] ( P )
- Return ?
OrdinaryDelete (O, P).
10.1.10.1 OrdinaryDelete ( O, P )
抽象操作 OrdinaryDelete は、引数 O（オブジェクト）、P（
- desc を ? O.[[GetOwnProperty]](P) とする。
- もし desc が
undefined なら、true を返す。 - もし desc.[[Configurable]] が
true なら、- O から名前 P の独自プロパティを削除する。
true を返す。
false を返す。
10.1.11 [[OwnPropertyKeys]] ( )
- Return
OrdinaryOwnPropertyKeys (O).
10.1.11.1 OrdinaryOwnPropertyKeys ( O )
抽象操作 OrdinaryOwnPropertyKeys は、引数 O（オブジェクト）を取り、
10.1.12 OrdinaryObjectCreate ( proto [ , additionalInternalSlotsList ] )
抽象操作 OrdinaryObjectCreate は、引数 proto（オブジェクトまたは
- internalSlotsList を « [[Prototype]], [[Extensible]] » とする。
- もし additionalInternalSlotsList が存在するなら、internalSlotsList を
リスト結合 により internalSlotsList と additionalInternalSlotsList の連結結果に設定する。 - O を
MakeBasicObject (internalSlotsList) とする。 - O.[[Prototype]] を proto に設定する。
- O を返す。
OrdinaryObjectCreate は
10.1.13 OrdinaryCreateFromConstructor ( constructor, intrinsicDefaultProto [ , internalSlotsList ] )
抽象操作 OrdinaryCreateFromConstructor は、引数 constructor（
保証 ：intrinsicDefaultProto はこの仕様のインストリンシックオブジェクト名であり、対応するオブジェクトはオブジェクトの [[Prototype]] 値として使用することを意図したインストリンシックでなければならない。- proto を ?
GetPrototypeFromConstructor (constructor, intrinsicDefaultProto) とする。 - もし internalSlotsList が存在するなら、slotsList を internalSlotsList とする。
- それ以外の場合、slotsList を新たな空の
List とする。 - Return
OrdinaryObjectCreate (proto, slotsList)。
10.1.14 GetPrototypeFromConstructor ( constructor, intrinsicDefaultProto )
抽象操作 GetPrototypeFromConstructor は、引数 constructor（
保証 ：intrinsicDefaultProto はこの仕様のインストリンシックオブジェクト名であり、対応するオブジェクトはオブジェクトの [[Prototype]] 値として使用することを意図したインストリンシックでなければならない。- proto を ?
Get (constructor,"prototype" ) とする。 - もし proto
がオブジェクトでない なら、- realm を ?
GetFunctionRealm (constructor) とする。 - proto を realm の intrinsicDefaultProto という名前のインストリンシックオブジェクトに設定する。
- realm を ?
- proto を返す。
constructor が [[Prototype]] 値を提供しない場合、使用されるデフォルト値は
constructor 関数の
10.1.15 RequireInternalSlot ( O, internalSlot )
抽象操作RequireInternalSlotは、引数O（
- もしOが
オブジェクトでない なら、TypeError 例外をスローする。 - もしOがinternalSlot内部スロットを持たないなら、
TypeError 例外をスローする。 unused を返す。
10.2 ECMAScript関数オブジェクト
ECMAScriptの
[[Extensible]]および[[Prototype]]に加え、ECMAScript
| 内部スロット | 型 | 説明 |
|---|---|---|
| [[Environment]] |
|
この関数がクロージャした |
| [[PrivateEnvironment]] |
|
この関数がクロージャした |
| [[FormalParameters]] |
|
関数の仮引数リストを定義するソーステキストのルート構文ノード。 |
| [[ECMAScriptCode]] |
|
関数本体を定義するソーステキストのルート構文ノード。 |
| [[ConstructorKind]] |
|
この関数が派生クラスの |
| [[Realm]] |
|
この関数が作成された |
| [[ScriptOrModule]] |
|
この関数が作成されたスクリプトまたはモジュール。 |
| [[ThisMode]] |
|
関数の仮引数および本体内でthis参照がどのように解釈されるかを定義する。thisがレキシカルに囲んでいる関数の |
| [[Strict]] | Boolean |
|
| [[HomeObject]] | オブジェクト |
関数がsuperを使用する場合、superプロパティ検索の起点となるオブジェクトの[[GetPrototypeOf]]を提供するオブジェクト。
|
| [[SourceText]] | Unicodeコードポイント列 |
関数を定義する |
| [[Fields]] |
|
関数がクラスである場合、クラスの非staticフィールドおよびそれに対応する初期化子を表す |
| [[PrivateMethods]] |
|
関数がクラスである場合、クラスの非staticなプライベートメソッドとアクセサを表すリスト。 |
| [[ClassFieldInitializerName]] |
文字列、シンボル、 |
関数がクラスフィールドの初期化子として生成された場合、そのフィールドの |
| [[IsClassConstructor]] | Boolean |
関数がクラスの |
すべてのECMAScript
10.2.1 [[Call]] ( thisArgument, argumentsList )
ECMAScriptの
- callerContextを
実行中の実行コンテキスト とする。 - calleeContextを
PrepareForOrdinaryCall (F,undefined )とする。 保証 ：calleeContextは現在実行中の実行コンテキスト である。- もしF.[[IsClassConstructor]]が
true なら、- errorを新しく生成した
TypeError オブジェクトとする。 - 注：errorはcalleeContext内で、Fに関連付けられた
Realm Record で作成される。 - calleeContextを
実行コンテキストスタック から除去し、callerContextを実行中の実行コンテキスト として復元する。 ThrowCompletion (error)を返す。
- errorを新しく生成した
OrdinaryCallBindThis (F, calleeContext, thisArgument)を実行する。- resultを
Completion (OrdinaryCallEvaluateBody (F, argumentsList))とする。 - calleeContextを
実行コンテキストスタック から除去し、callerContextを実行中の実行コンテキスト として復元する。 - もしresultが
return completion なら、result.[[Value]]を返す。 保証 ：resultはthrow completion である。- ? resultを返す。
ステップ
10.2.1.1 PrepareForOrdinaryCall ( F, newTarget )
抽象操作PrepareForOrdinaryCallは、引数F（ECMAScript
- callerContextを
実行中の実行コンテキスト とする。 - calleeContextを新しい
ECMAScriptコード実行コンテキスト とする。 - calleeContextのFunctionをFに設定する。
- calleeRealmをF.[[Realm]]とする。
- calleeContextの
Realm をcalleeRealmに設定する。 - calleeContextのScriptOrModuleをF.[[ScriptOrModule]]に設定する。
- localEnvを
NewFunctionEnvironment (F, newTarget)とする。 - calleeContextのLexicalEnvironmentをlocalEnvに設定する。
- calleeContextのVariableEnvironmentをlocalEnvに設定する。
- calleeContextのPrivateEnvironmentをF.[[PrivateEnvironment]]に設定する。
- もしcallerContextがすでにサスペンドされていなければ、callerContextをサスペンドする。
- calleeContextを
実行コンテキストスタック にプッシュする；calleeContextは現在の実行中の実行コンテキスト である。 - 注：この時点以降に生成される例外オブジェクトはcalleeRealmに関連付けられる。
- calleeContextを返す。
10.2.1.2 OrdinaryCallBindThis ( F, calleeContext, thisArgument )
抽象操作OrdinaryCallBindThisは、引数F（ECMAScript
- thisModeをF.[[ThisMode]]とする。
- もしthisModeが
lexical なら、unused を返す。 - calleeRealmをF.[[Realm]]とする。
- localEnvをcalleeContextのLexicalEnvironmentとする。
- もしthisModeが
strict なら、- thisValueをthisArgumentとする。
- それ以外の場合、
- もしthisArgumentが
undefined またはnull のいずれかなら、- globalEnvをcalleeRealm.[[GlobalEnv]]とする。
保証 ：globalEnvはグローバル環境レコード である。- thisValueをglobalEnv.[[GlobalThisValue]]とする。
- それ以外の場合、
- もしthisArgumentが
保証 ：localEnvは関数環境レコード である。保証 ：次のステップはlocalEnv.[[ThisBindingStatus]]がinitialized でないのでabrupt completion を返すことはない。- !
BindThisValue (localEnv, thisValue)を実行する。 unused を返す。
10.2.1.3 ランタイムセマンティクス: EvaluateBody
- ?
EvaluateFunctionBody ofFunctionBody を、引数functionObjectおよびargumentsListで呼び出して返す。
- ?
EvaluateConciseBody ofConciseBody を、引数functionObjectおよびargumentsListで呼び出して返す。
- ?
EvaluateGeneratorBody ofGeneratorBody を、引数functionObjectおよびargumentsListで呼び出して返す。
- ?
EvaluateAsyncGeneratorBody ofAsyncGeneratorBody を、引数functionObjectおよびargumentsListで呼び出して返す。
- ?
EvaluateAsyncFunctionBody ofAsyncFunctionBody を、引数functionObjectおよびargumentsListで呼び出して返す。
- ?
EvaluateAsyncConciseBody ofAsyncConciseBody を、引数functionObjectおよびargumentsListで呼び出して返す。
保証 ：argumentsListは空である。保証 ：functionObject.[[ClassFieldInitializerName]]はempty でない。- もし
IsAnonymousFunctionDefinition (AssignmentExpression )がtrue なら、- valueを?
NamedEvaluation ofInitializer を、引数functionObject.[[ClassFieldInitializerName]]で呼び出して得る。
- valueを?
- それ以外の場合、
- rhsを?
Evaluation ofAssignmentExpression で呼び出して得る。 - valueを?
GetValue (rhs)で得る。
- rhsを?
ReturnCompletion (value)を返す。
フィールド初期化子は関数境界を構成するが、
保証 ：argumentsListは空である。- ?
EvaluateClassStaticBlockBody ofClassStaticBlockBody を引数functionObjectで呼び出して返す。
10.2.1.4 OrdinaryCallEvaluateBody ( F, argumentsList )
抽象操作OrdinaryCallEvaluateBodyは引数F（ECMAScript
- ?
EvaluateBody of F.[[ECMAScriptCode]] を、引数FおよびargumentsListで呼び出して返す。
10.2.2 [[Construct]] ( argumentsList, newTarget )
ECMAScriptの
- callerContextを
実行中の実行コンテキスト とする。 - kindをF.[[ConstructorKind]]とする。
- もしkindが
base なら、- thisArgumentを?
OrdinaryCreateFromConstructor (newTarget,"%Object.prototype%" )とする。
- thisArgumentを?
- calleeContextを
PrepareForOrdinaryCall (F, newTarget)とする。 保証 ：calleeContextは現在実行中の実行コンテキスト である。- もしkindが
base なら、OrdinaryCallBindThis (F, calleeContext, thisArgument)を実行する。- initializeResultを
Completion (InitializeInstanceElements (thisArgument, F))とする。 - もしinitializeResultが
abrupt completion なら、- calleeContextを
実行コンテキストスタック から除去し、callerContextを実行中の実行コンテキスト として復元する。 - ? initializeResultを返す。
- calleeContextを
- constructorEnvをcalleeContextのLexicalEnvironmentとする。
- resultを
Completion (OrdinaryCallEvaluateBody (F, argumentsList))とする。 - calleeContextを
実行コンテキストスタック から除去し、callerContextを実行中の実行コンテキスト として復元する。 - もしresultが
throw completion なら、- ? resultを返す。
保証 ：resultはreturn completion である。- もしresult.[[Value]]が
オブジェクトである なら、result.[[Value]]を返す。 - もしkindが
base なら、thisArgumentを返す。 - もしresult.[[Value]]が
undefined でないなら、TypeError 例外をスローする。 - thisBindingを? constructorEnv.GetThisBinding()とする。
保証 ：thisBindingはオブジェクトである 。- thisBindingを返す。
10.2.3 OrdinaryFunctionCreate ( functionPrototype, sourceText, ParameterList, Body, thisMode, env, privateEnv )
抽象操作OrdinaryFunctionCreateは、引数functionPrototype（オブジェクト）、sourceText（Unicodeコードポイント列）、ParameterList（
- internalSlotsListを
表30 に示す内部スロットとする。 - Fを
OrdinaryObjectCreate (functionPrototype, internalSlotsList)とする。 - F.[[Call]]を
10.2.1 で規定される定義に設定する。 - F.[[SourceText]]をsourceTextに設定する。
- F.[[FormalParameters]]をParameterListに設定する。
- F.[[ECMAScriptCode]]をBodyに設定する。
- Strictを
IsStrict (Body)とする。 - F.[[Strict]]をStrictに設定する。
- もしthisModeが
lexical-this なら、F.[[ThisMode]]をlexical に設定する。 - それ以外でStrictが
true なら、F.[[ThisMode]]をstrict に設定する。 - それ以外の場合、F.[[ThisMode]]を
global に設定する。 - F.[[IsClassConstructor]]を
false に設定する。 - F.[[Environment]]をenvに設定する。
- F.[[PrivateEnvironment]]をprivateEnvに設定する。
- F.[[ScriptOrModule]]を
GetActiveScriptOrModule ()に設定する。 - F.[[Realm]]を
現在のRealm Record に設定する。 - F.[[HomeObject]]を
undefined に設定する。 - F.[[Fields]]を新たな空の
List に設定する。 - F.[[PrivateMethods]]を新たな空の
List に設定する。 - F.[[ClassFieldInitializerName]]を
empty に設定する。 - lenを
ExpectedArgumentCount of ParameterListとする。 SetFunctionLength (F, len)を実行する。- Fを返す。
10.2.4 AddRestrictedFunctionProperties ( F, realm )
抽象操作AddRestrictedFunctionPropertiesは、引数F（
保証 ：realm.[[Intrinsics]].[[%ThrowTypeError% ]]が存在し初期化されている。- throwerをrealm.[[Intrinsics]].[[
%ThrowTypeError% ]]とする。 - !
DefinePropertyOrThrow (F,"caller" , PropertyDescriptor { [[Get]]: thrower, [[Set]]: thrower, [[Enumerable]]:false , [[Configurable]]:true }) を実行する。 - !
DefinePropertyOrThrow (F,"arguments" , PropertyDescriptor { [[Get]]: thrower, [[Set]]: thrower, [[Enumerable]]:false , [[Configurable]]:true }) を実行する。 unused を返す。
10.2.4.1 %ThrowTypeError% ( )
この関数は%ThrowTypeError%固有オブジェクトである。
これは各
呼び出されたとき、次の手順を実行する：
TypeError 例外をスローする。
この関数の[[Extensible]]内部スロットの値は
この関数の
この関数の
10.2.5 MakeConstructor ( F [ , writablePrototype [ , prototype ] ] )
抽象操作MakeConstructorは、引数F（ECMAScript
- もしFがECMAScript
関数オブジェクト なら、保証 ：IsConstructor (F)はfalse 。保証 ：Fは拡張可能なオブジェクトであり、かつ"prototype" 独自プロパティを持たない。- F.[[Construct]]を
10.2.2 で規定される定義に設定する。
- それ以外の場合、
- F.[[Construct]]を
10.3.2 で規定される定義に設定する。
- F.[[Construct]]を
- F.[[ConstructorKind]]を
base に設定する。 - もしwritablePrototypeが指定されていなければ、writablePrototypeを
true に設定する。 - もしprototypeが指定されていなければ、
- prototypeを
OrdinaryObjectCreate (%Object.prototype% )に設定する。 - !
DefinePropertyOrThrow (prototype,"constructor" , PropertyDescriptor { [[Value]]: F, [[Writable]]: writablePrototype, [[Enumerable]]:false , [[Configurable]]:true }) を実行する。
- prototypeを
- !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]: writablePrototype, [[Enumerable]]:false , [[Configurable]]:false }) を実行する。 unused を返す。
10.2.6 MakeClassConstructor ( F )
抽象操作MakeClassConstructorは、引数F（ECMAScript
保証 ：F.[[IsClassConstructor]]はfalse である。- F.[[IsClassConstructor]]を
true に設定する。 unused を返す。
10.2.7 MakeMethod ( F, homeObject )
抽象操作MakeMethodは、引数F（ECMAScript
10.2.8 DefineMethodProperty ( homeObject, key, closure, enumerable )
抽象操作DefineMethodPropertyは、引数homeObject（オブジェクト）、key（
保証 ：homeObjectは通常かつ拡張可能なオブジェクトである。- もしkeyが
Private Name なら、PrivateElement { [[Key]]: key, [[Kind]]:method , [[Value]]: closure } を返す。
- それ以外の場合、
- descをPropertyDescriptor { [[Value]]:
closure, [[Writable]]:
true , [[Enumerable]]: enumerable, [[Configurable]]:true } とする。 - ?
DefinePropertyOrThrow (homeObject, key, desc)を実行する。 - 注：
DefinePropertyOrThrow がabrupt completion を返すのは、クラスstaticメソッドでkeyが"prototype" の場合のみである。 unused を返す。
- descをPropertyDescriptor { [[Value]]:
closure, [[Writable]]:
10.2.9 SetFunctionName ( F, name [ , prefix ] )
抽象操作SetFunctionNameは、引数F（
保証 ：Fは拡張可能なオブジェクトであり、"name" 独自プロパティを持たない。- もしnameが
シンボルである なら、- descriptionをnameの[[Description]]値とする。
- もしdescriptionが
undefined なら、nameを空文字列に設定する。 - それ以外の場合、nameを
文字列連結 で"[" 、description、"]" を連結したものに設定する。
- それ以外でnameが
Private Name なら、- nameをname.[[Description]]に設定する。
- もしFが[[InitialName]]内部スロットを持つなら、
- F.[[InitialName]]をnameに設定する。
- もしprefixが指定されているなら、
- nameを
文字列連結 でprefix、コード単位0x0020（SPACE）、nameを連結したものに設定する。 - もしFが[[InitialName]]内部スロットを持つなら、
- （任意で）F.[[InitialName]]をnameに設定してもよい。
- nameを
- !
DefinePropertyOrThrow (F,"name" , PropertyDescriptor { [[Value]]: name, [[Writable]]:false , [[Enumerable]]:false , [[Configurable]]:true }) を実行する。 unused を返す。
10.2.10 SetFunctionLength ( F, length )
抽象操作SetFunctionLengthは、引数F（
保証 ：Fは拡張可能なオブジェクトであり、"length" 独自プロパティを持たない。- !
DefinePropertyOrThrow (F,"length" , PropertyDescriptor { [[Value]]:𝔽 (length), [[Writable]]:false , [[Enumerable]]:false , [[Configurable]]:true }) を実行する。 unused を返す。
10.2.11 FunctionDeclarationInstantiation ( func, argumentsList )
抽象操作FunctionDeclarationInstantiationは、引数func（ECMAScript
呼び出されたとき、次の手順を実行する：
- calleeContextを
実行中の実行コンテキスト とする。 - codeをfunc.[[ECMAScriptCode]]とする。
- strictをfunc.[[Strict]]とする。
- formalsをfunc.[[FormalParameters]]とする。
- parameterNamesを
BoundNames of formalsとする。 - もしparameterNamesに重複があれば、hasDuplicatesを
true 、なければfalse とする。 - simpleParameterListを
IsSimpleParameterList of formalsとする。 - hasParameterExpressionsを
ContainsExpression of formalsとする。 - varNamesを
VarDeclaredNames of codeとする。 - varDeclarationsを
VarScopedDeclarations of codeとする。 - lexicalNamesを
LexicallyDeclaredNames of codeとする。 - functionNamesを新しい空の
List とする。 - functionsToInitializeを新しい空の
List とする。 - varDeclarationsの各要素dについて、逆順で、以下を行う：
- もしdが
VariableDeclaration でもForBinding でもBindingIdentifier でもない場合、保証 ：dはFunctionDeclaration 、GeneratorDeclaration 、AsyncFunctionDeclaration 、またはAsyncGeneratorDeclaration のいずれかである。- fnを
BoundNames of dの唯一の要素とする。 - もしfunctionNamesがfnを含まないなら、
- fnをfunctionNamesの先頭に挿入する。
- 注：同じ名前の関数宣言が複数ある場合、最後の宣言が使用される。
- dをfunctionsToInitializeの先頭に挿入する。
- もしdが
- argumentsObjectNeededを
true とする。 - もしfunc.[[ThisMode]]が
lexical なら、- 注：アロー関数はargumentsオブジェクトを持たない。
- argumentsObjectNeededを
false に設定する。
- それ以外でparameterNamesが
"arguments" を含む場合、- argumentsObjectNeededを
false に設定する。
- argumentsObjectNeededを
- それ以外でhasParameterExpressionsが
false の場合、- もしfunctionNamesが
"arguments" を含むかlexicalNamesが"arguments" を含むなら、- argumentsObjectNeededを
false に設定する。
- argumentsObjectNeededを
- もしfunctionNamesが
- もしstrictが
true またはhasParameterExpressionsがfalse なら、- 注：パラメータ用には1つの
環境レコード だけが必要。strictモードコード内でのevalの呼び出しは、そのevalの外側で見える新しい束縛を作成できないため。 - envをcalleeContextのLexicalEnvironmentとする。
- 注：パラメータ用には1つの
- それ以外の場合、
- 注：仮引数リスト内のdirect eval呼び出しで作成される束縛がパラメータ宣言環境の外側になるよう、別の
環境レコード が必要となる。 - calleeEnvをcalleeContextのLexicalEnvironmentとする。
- envを
NewDeclarativeEnvironment (calleeEnv)とする。 保証 ：calleeContextのVariableEnvironmentとcalleeEnvは同じ環境レコード である。- calleeContextのLexicalEnvironmentをenvに設定する。
- 注：仮引数リスト内のdirect eval呼び出しで作成される束縛がパラメータ宣言環境の外側になるよう、別の
- parameterNamesの各文字列paramNameについて、以下を行う：
- もしargumentsObjectNeededが
true なら、- もしstrictが
true またはsimpleParameterListがfalse なら、- aoを
CreateUnmappedArgumentsObject (argumentsList)とする。
- aoを
- それ以外の場合、
- 注：マップドargumentsオブジェクトは、restパラメータやパラメータデフォルト値初期化子、分割代入パラメータを持たない
非厳格関数 でのみ提供される。 - aoを
CreateMappedArgumentsObject (func, formals, argumentsList, env)とする。
- 注：マップドargumentsオブジェクトは、restパラメータやパラメータデフォルト値初期化子、分割代入パラメータを持たない
- もしstrictが
true なら、- ! env.CreateImmutableBinding(
"arguments" ,false )を実行する。 - 注：
strictモードコード では早期エラー により、この束縛への代入は試みられないため、そのミュータビリティは観測できない。
- ! env.CreateImmutableBinding(
- それ以外の場合、
- ! env.CreateMutableBinding(
"arguments" ,false )を実行する。
- ! env.CreateMutableBinding(
- ! env.InitializeBinding(
"arguments" , ao)を実行する。 - parameterBindingsを
list-concatenation of parameterNamesと«"arguments" »とする。
- もしstrictが
- それ以外の場合、
- parameterBindingsをparameterNamesとする。
- iteratorRecordを
CreateListIteratorRecord (argumentsList)とする。 - もしhasDuplicatesが
true なら、- usedEnvを
undefined とする。
- usedEnvを
- それ以外の場合、
- usedEnvをenvとする。
- 注：次のステップは、式位置で
ReturnCompletion を返すことはできない。なぜならそのようなcompletionはYieldExpression の使用のみで発生しうるが、これは早期エラー規則(15.5.1 ,15.6.1 )によってパラメータリスト内で禁止されている。 - ?
IteratorBindingInitialization of formals with arguments iteratorRecord and usedEnvを実行する。 - もしhasParameterExpressionsが
false なら、 - それ以外の場合、
- 注：仮引数リスト内の式で作成されるクロージャが関数本体の宣言を見ることができないよう、別の
環境レコード が必要。 - varEnvを
NewDeclarativeEnvironment (env)とする。 - calleeContextのVariableEnvironmentをvarEnvに設定する。
- instantiatedVarNamesを新しい空の
List とする。 - varNamesの各要素nについて、
- もしinstantiatedVarNamesがnを含まないなら、
- nをinstantiatedVarNamesに追加する。
- ! varEnv.CreateMutableBinding(n,
false )を実行する。 - もしparameterBindingsがnを含まないか、またはfunctionNamesがnを含むなら、
- initialValueを
undefined とする。
- initialValueを
- それ以外の場合、
- initialValueを!
env.GetBindingValue(n,
false )とする。
- initialValueを!
env.GetBindingValue(n,
- ! varEnv.InitializeBinding(n, initialValue)を実行する。
- 注：仮引数と同じ名前のvarは、初期状態で対応する初期化済みパラメータと同じ値を持つ。
- もしinstantiatedVarNamesがnを含まないなら、
- 注：仮引数リスト内の式で作成されるクロージャが関数本体の宣言を見ることができないよう、別の
- 注：付録
B.3.2.1 がこの地点で追加のステップを挿入する。 - もしstrictが
false なら、- lexEnvを
NewDeclarativeEnvironment (varEnv)とする。 - 注：
非厳格関数 はトップレベルのレキシカル宣言のために別の環境レコード を使う。こうすることでdirect eval がevalコードで導入されたvarスコープ宣言が既存のトップレベルレキシカルスコープ宣言と衝突するかどうか判定できる。これはstrict関数 では不要であり、strictなdirect eval は常に全ての宣言を新しい環境レコード に配置するためである。
- lexEnvを
- それ以外の場合、
- lexEnvをvarEnvとする。
- calleeContextのLexicalEnvironmentをlexEnvに設定する。
- lexDeclarationsを
LexicallyScopedDeclarations of codeとする。 - lexDeclarationsの各要素dについて、以下を行う：
- 注：レキシカル宣言名は関数/ジェネレーター宣言、仮引数、var名と重複しない。レキシカル宣言名はここでインスタンス化されるが初期化はされない。
BoundNames of dの各要素dnについて、- もし
IsConstantDeclaration of dがtrue なら、- ! lexEnv.CreateImmutableBinding(dn,
true )を実行する。
- ! lexEnv.CreateImmutableBinding(dn,
- それ以外の場合、
- ! lexEnv.CreateMutableBinding(dn,
false )を実行する。
- ! lexEnv.CreateMutableBinding(dn,
- もし
- privateEnvをcalleeContextのPrivateEnvironmentとする。
- functionsToInitializeの各
Parse Node fについて、- fnを
BoundNames of fの唯一の要素とする。 - foを
InstantiateFunctionObject of f with arguments lexEnvとprivateEnvとする。 - ! varEnv.SetMutableBinding(fn, fo,
false )を実行する。
- fnを
unused を返す。
10.3 組み込み関数オブジェクト
組み込み
すべての
- [[Realm]]：関数が作成された
Realm Record 。これはrealm を表す。 - [[InitialName]]：関数の初期名となる文字列。
20.2.3.5 で使用される。
組み込み
組み込み
組み込み
実装は、本仕様で定義されていない追加の組み込み
10.3.1 [[Call]] ( thisArgument, argumentsList )
組み込み
- ?
BuiltinCallOrConstruct (F, thisArgument, argumentsList,undefined )を返す。
10.3.2 [[Construct]] ( argumentsList, newTarget )
組み込み
- resultを?
BuiltinCallOrConstruct (F,uninitialized , argumentsList, newTarget)とする。 保証 ：resultはオブジェクトである 。- resultを返す。
10.3.3 BuiltinCallOrConstruct ( F, thisArgument, argumentsList, newTarget )
抽象操作BuiltinCallOrConstructは、引数F（組み込み
- callerContextを
実行中の実行コンテキスト とする。 - もしcallerContextがすでにサスペンドされていなければ、callerContextをサスペンドする。
- calleeContextを新しい
実行コンテキスト とする。 - calleeContextのFunctionをFに設定する。
- calleeRealmをF.[[Realm]]とする。
- calleeContextの
Realm をcalleeRealmに設定する。 - calleeContextのScriptOrModuleを
null に設定する。 - calleeContextに対して必要な
実装依存 の初期化を実行する。 - calleeContextを
実行コンテキストスタック にプッシュする；calleeContextは現在の実行中の実行コンテキスト である。 - resultを
Completion Record とし、「Fを評価する」ことにより得られる。仕様で定めるように、thisArgumentがuninitialized ならthis 値は初期化されない。それ以外の場合はthisArgumentがthis 値となる。argumentsListは指定されたパラメータを与え、newTargetはNewTarget値を与える。 - 注：Fが本ドキュメントで定義されている場合、「Fの仕様」とは、ステップあるいはその他の手段で規定されるその挙動である。
- calleeContextを
実行コンテキストスタック から除去し、callerContextを実行中の実行コンテキスト として復元する。 - ? resultを返す。
calleeContextが
10.3.4 CreateBuiltinFunction ( behaviour, length, name, additionalInternalSlotsList [ , realm [ , prototype [ , prefix ] ] ] )
抽象操作CreateBuiltinFunctionは、引数behaviour（
- もしrealmが指定されていなければ、realmを
現在のRealm Record に設定する。 - もしprototypeが指定されていなければ、prototypeをrealm.[[Intrinsics]].[[
%Function.prototype% ]]に設定する。 - internalSlotsListを
List とし、これから作成する組み込み関数オブジェクト に10.3 が要求するすべての内部スロット名を入れる。 - internalSlotsListにadditionalInternalSlotsListの要素を追加する。
- funcを新しい組み込み
関数オブジェクト とし、呼び出されたときbehaviourで規定された動作を、指定された引数をbehaviourで指定されたパラメータ値として用いて実行するものとする。新しい関数オブジェクト はinternalSlotsListの名前を持つ内部スロットと、[[InitialName]]内部スロットを持つ。 - func.[[Prototype]]をprototypeに設定する。
- func.[[Extensible]]を
true に設定する。 - func.[[Realm]]をrealmに設定する。
- func.[[InitialName]]を
null に設定する。 SetFunctionLength (func, length)を実行する。- もしprefixが指定されていなければ、
SetFunctionName (func, name)を実行する。
- それ以外の場合、
SetFunctionName (func, name, prefix)を実行する。
- funcを返す。
本仕様で定義される各組み込み関数は、CreateBuiltinFunction抽象操作の呼び出しにより生成される。
10.4 組み込みエキゾチックオブジェクトの内部メソッドとスロット
本仕様は複数の種類の組み込み
10.4.1 バウンド関数エキゾチックオブジェクト
あるオブジェクトがバウンド関数エキゾチックオブジェクトであるのは、その[[Call]]および（該当する場合）[[Construct]]内部メソッドが以下の実装を用い、それ以外の必須内部メソッドが
| 内部スロット | 型 | 説明 |
|---|---|---|
| [[BoundTargetFunction]] | 呼び出し可能オブジェクト |
ラップされている |
| [[BoundThis]] |
|
ラップされた関数を呼び出す際に常に |
| [[BoundArguments]] |
|
ラップされた関数への呼び出しで最初の引数として使用される値のリスト。 |
10.4.1.1 [[Call]] ( thisArgument, argumentsList )
- targetをF.[[BoundTargetFunction]]とする。
- boundThisをF.[[BoundThis]]とする。
- boundArgsをF.[[BoundArguments]]とする。
- argsを
list-concatenation of boundArgsとargumentsListとする。 - ?
Call (target, boundThis, args)を返す。
10.4.1.2 [[Construct]] ( argumentsList, newTarget )
- targetをF.[[BoundTargetFunction]]とする。
保証 ：IsConstructor (target)はtrue である。- boundArgsをF.[[BoundArguments]]とする。
- argsを
list-concatenation of boundArgsとargumentsListとする。 - もし
SameValue (F, newTarget)がtrue なら、newTargetをtargetとする。 - ?
Construct (target, args, newTarget)を返す。
10.4.1.3 BoundFunctionCreate ( targetFunction, boundThis, boundArgs )
抽象操作BoundFunctionCreateは、引数targetFunction（
- protoを? targetFunction.[[GetPrototypeOf]]()とする。
- internalSlotsListを
list-concatenation of « [[Prototype]], [[Extensible]] » および表31 に挙げられている内部スロットとする。 - objを
MakeBasicObject (internalSlotsList)とする。 - obj.[[Prototype]]をprotoに設定する。
- obj.[[Call]]を
10.4.1.1 で説明されるものに設定する。 - もし
IsConstructor (targetFunction)がtrue なら、- obj.[[Construct]]を
10.4.1.2 で説明されるものに設定する。
- obj.[[Construct]]を
- obj.[[BoundTargetFunction]]をtargetFunctionに設定する。
- obj.[[BoundThis]]をboundThisに設定する。
- obj.[[BoundArguments]]をboundArgsに設定する。
- objを返す。
10.4.2 配列エキゾチックオブジェクト
配列（Array）は、
あるオブジェクトの[[DefineOwnProperty]]内部メソッドが以下の実装を使い、それ以外の必須内部メソッドが
10.4.2.1 [[DefineOwnProperty]] ( P, Desc )
- もしPが
"length" なら、- ?
ArraySetLength (A, Desc)を返す。
- ?
- それ以外でPが
配列インデックス なら、- lengthDescを
OrdinaryGetOwnProperty (A,"length" )とする。 保証 ：lengthDescはundefined でない。保証 ：IsDataDescriptor (lengthDesc)はtrue 。保証 ：lengthDesc.[[Configurable]]はfalse 。- lengthをlengthDesc.[[Value]]とする。
保証 ：lengthは0以上の整数値(Number) である。- indexを!
ToUint32 (P)とする。 - もしindex ≥ lengthかつlengthDesc.[[Writable]]が
false なら、false を返す。 - succeededを!
OrdinaryDefineOwnProperty (A, P, Desc)とする。 - もしsucceededが
false なら、false を返す。 - もしindex ≥ lengthなら、
- lengthDesc.[[Value]]をindex +
1 𝔽に設定する。 - succeededを!
OrdinaryDefineOwnProperty (A,"length" , lengthDesc)とする。 保証 ：succeededはtrue 。
- lengthDesc.[[Value]]をindex +
true を返す。
- lengthDescを
- ?
OrdinaryDefineOwnProperty (A, P, Desc)を返す。
10.4.2.2 ArrayCreate ( length [ , proto ] )
抽象操作ArrayCreateは、引数length（0以上の
- もしlength > 232 - 1なら、
RangeError 例外をスローする。 - もしprotoが指定されていなければ、protoを
%Array.prototype% に設定する。 - Aを
MakeBasicObject (« [[Prototype]], [[Extensible]] »)とする。 - A.[[Prototype]]をprotoに設定する。
- A.[[DefineOwnProperty]]を
10.4.2.1 で規定されるものに設定する。 - !
OrdinaryDefineOwnProperty (A,"length" , PropertyDescriptor { [[Value]]:𝔽 (length), [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }) を実行する。 - Aを返す。
10.4.2.3 ArraySpeciesCreate ( originalArray, length )
抽象操作ArraySpeciesCreateは、引数originalArray（オブジェクト）、length（0以上の
- isArrayを?
IsArray (originalArray)とする。 - もしisArrayが
false なら、?ArrayCreate (length)を返す。 - Cを?
Get (originalArray,"constructor" )とする。 - もし
IsConstructor (C)がtrue なら、- thisRealmを
現在のRealm Record とする。 - realmCを?
GetFunctionRealm (C)とする。 - もしthisRealmとrealmCが同じ
Realm Record でないなら、
- thisRealmを
- もしCが
オブジェクトである なら、- Cを?
Get (C,%Symbol.species% )に設定する。 - もしCが
null なら、Cをundefined に設定する。
- Cを?
- もしCが
undefined なら、?ArrayCreate (length)を返す。 - もし
IsConstructor (C)がfalse なら、TypeError 例外をスローする。 - ?
Construct (C, «𝔽 (length) »)を返す。
もしoriginalArrayが現在のArray.prototypeメソッドがArraySpeciesCreateで定義されるようになったWebブラウザとの互換性を維持する。
10.4.2.4 ArraySetLength ( A, Desc )
抽象操作ArraySetLengthは、引数A（配列）、Desc（
- もしDescが[[Value]]フィールドを持たないなら、
- !
OrdinaryDefineOwnProperty (A,"length" , Desc)を返す。
- !
- newLenDescをDescのコピーとする。
- newLenを?
ToUint32 (Desc.[[Value]])とする。 - numberLenを?
ToNumber (Desc.[[Value]])とする。 - もし
SameValueZero (newLen, numberLen)がfalse なら、RangeError 例外をスローする。 - newLenDesc.[[Value]]をnewLenに設定する。
- oldLenDescを
OrdinaryGetOwnProperty (A,"length" )とする。 保証 ：oldLenDescはundefined でない。保証 ：IsDataDescriptor (oldLenDesc)はtrue 。保証 ：oldLenDesc.[[Configurable]]はfalse である。- oldLenをoldLenDesc.[[Value]]とする。
- もしnewLen ≥ oldLenなら、
- !
OrdinaryDefineOwnProperty (A,"length" , newLenDesc)を返す。
- !
- もしoldLenDesc.[[Writable]]が
false なら、false を返す。 - もしnewLenDescが[[Writable]]フィールドを持たないかnewLenDesc.[[Writable]]が
true なら、- newWritableを
true とする。
- newWritableを
- それ以外の場合、
- 注：[[Writable]]属性を
false に設定するのは、要素の削除に失敗した場合に遅延される。 - newWritableを
false とする。 - newLenDesc.[[Writable]]を
true に設定する。
- 注：[[Writable]]属性を
- succeededを!
OrdinaryDefineOwnProperty (A,"length" , newLenDesc)とする。 - もしsucceededが
false なら、false を返す。 - Aのすべての自身の
プロパティキー Pについて、Pが配列インデックス かつ!ToUint32 (P) ≥ newLenであるものを降順で、以下を行う：- deleteSucceededを! A.[[Delete]](P)とする。
- もしdeleteSucceededが
false なら、- newLenDesc.[[Value]]を!
ToUint32 (P) +1 𝔽に設定する。 - もしnewWritableが
false なら、newLenDesc.[[Writable]]をfalse に設定する。 - !
OrdinaryDefineOwnProperty (A,"length" , newLenDesc)を実行する。 false を返す。
- newLenDesc.[[Value]]を!
- もしnewWritableが
false なら、- succeededを!
OrdinaryDefineOwnProperty (A,"length" , PropertyDescriptor { [[Writable]]:false })とする。 保証 ：succeededはtrue である。
- succeededを!
true を返す。
10.4.3 文字列エキゾチックオブジェクト
Stringオブジェクトは、文字列値をカプセル化し、その文字列値の個々のコードユニット要素に対応する仮想の
あるオブジェクトの[[GetOwnProperty]]、[[DefineOwnProperty]]、[[OwnPropertyKeys]]内部メソッドが以下の実装を使い、それ以外の必須内部メソッドが
10.4.3.1 [[GetOwnProperty]] ( P )
- descを
OrdinaryGetOwnProperty (S, P)とする。 - もしdescが
undefined でなければ、descを返す。 StringGetOwnProperty (S, P)を返す。
10.4.3.2 [[DefineOwnProperty]] ( P, Desc )
- stringDescを
StringGetOwnProperty (S, P)とする。 - もしstringDescが
undefined でなければ、- extensibleをS.[[Extensible]]とする。
IsCompatiblePropertyDescriptor (extensible, Desc, stringDesc)を返す。
- !
OrdinaryDefineOwnProperty (S, P, Desc)を返す。
10.4.3.3 [[OwnPropertyKeys]] ( )
- keysを新しい空の
List とする。 - strをO.[[StringData]]とする。
保証 ：strは文字列である 。- lenをstrの長さとする。
- 0 ≤ i < len となる各
整数 iについて、昇順で： - Oの自身の
プロパティキー Pについて、Pが配列インデックス かつ!ToIntegerOrInfinity (P) ≥ lenであるものを昇順で：- Pをkeysに追加する。
- Oの自身の
プロパティキー Pについて、Pが文字列である かつPが配列インデックス でないものを生成順に昇順で：- Pをkeysに追加する。
- Oの自身の
プロパティキー Pについて、Pがシンボルである ものを生成順に昇順で：- Pをkeysに追加する。
- keysを返す。
10.4.3.4 StringCreate ( value, prototype )
抽象操作StringCreateは、引数value（文字列）、prototype（オブジェクト）を取り、
- Sを
MakeBasicObject (« [[Prototype]], [[Extensible]], [[StringData]] »)とする。 - S.[[Prototype]]をprototypeに設定する。
- S.[[StringData]]をvalueに設定する。
- S.[[GetOwnProperty]]を
10.4.3.1 で規定されるものに設定する。 - S.[[DefineOwnProperty]]を
10.4.3.2 で規定されるものに設定する。 - S.[[OwnPropertyKeys]]を
10.4.3.3 で規定されるものに設定する。 - lengthをvalueの長さとする。
- !
DefinePropertyOrThrow (S,"length" , PropertyDescriptor { [[Value]]:𝔽 (length), [[Writable]]:false , [[Enumerable]]:false , [[Configurable]]:false }) を実行する。 - Sを返す。
10.4.3.5 StringGetOwnProperty ( S, P )
抽象操作StringGetOwnPropertyは、引数S（[[StringData]]内部スロットを持つオブジェクト）、P（
- もしPが
文字列でない なら、undefined を返す。 - indexを
CanonicalNumericIndexString (P)とする。 - もしindexが
整数値(Number) でなければ、undefined を返す。 - もしindexが
-0 𝔽またはindex <-0 𝔽なら、undefined を返す。 - strをS.[[StringData]]とする。
保証 ：strは文字列である 。- lenをstrの長さとする。
- もし
ℝ (index) ≥ lenなら、undefined を返す。 - resultStrをstrの
substring （ℝ (index)からℝ (index)+1まで）とする。 - プロパティディスクリプタ{ [[Value]]: resultStr, [[Writable]]:
false , [[Enumerable]]:true , [[Configurable]]:false }を返す。
10.4.4 Argumentsエキゾチックオブジェクト
ほとんどのECMAScript関数は、コードで利用可能なargumentsオブジェクトを生成する。関数定義の特性によって、そのargumentsオブジェクトは
オブジェクトが、ここで明示されていない内部メソッドについて
Object.prototype.toString（
ParameterMapオブジェクトとそのプロパティ値は、argumentsオブジェクトと引数束縛の連動を規定するための仕組みとして用いられる。ParameterMapオブジェクトおよびそのプロパティ値となるオブジェクトは、ECMAScriptコードから直接観測できない。ECMAScript実装は、規定されたセマンティクスを実装するために実際にこれらのオブジェクトを生成・利用する必要はない。
通常のargumentsオブジェクトは、アクセス時に
ECMAScript実装の
10.4.4.1 [[GetOwnProperty]] ( P )
- descを
OrdinaryGetOwnProperty (args, P)とする。 - もしdescが
undefined なら、undefined を返す。 - mapをargs.[[ParameterMap]]とする。
- isMappedを!
HasOwnProperty (map, P)とする。 - もしisMappedが
true なら、- desc.[[Value]]を!
Get (map, P)に設定する。
- desc.[[Value]]を!
- descを返す。
10.4.4.2 [[DefineOwnProperty]] ( P, Desc )
- mapをargs.[[ParameterMap]]とする。
- isMappedを!
HasOwnProperty (map, P)とする。 - newArgDescをDescとする。
- もしisMappedが
true かつIsDataDescriptor (Desc)がtrue なら、- もしDescが[[Value]]フィールドを持たず、Descが[[Writable]]フィールドを持ち、Desc.[[Writable]]が
false なら、- newArgDescをDescのコピーとする。
- newArgDesc.[[Value]]を!
Get (map, P)に設定する。
- もしDescが[[Value]]フィールドを持たず、Descが[[Writable]]フィールドを持ち、Desc.[[Writable]]が
- allowedを!
OrdinaryDefineOwnProperty (args, P, newArgDesc)とする。 - もしallowedが
false なら、false を返す。 - もしisMappedが
true なら、- もし
IsAccessorDescriptor (Desc)がtrue なら、- ! map.[[Delete]](P)を実行する。
- それ以外の場合、
- もし
true を返す。
10.4.4.3 [[Get]] ( P, Receiver )
- mapをargs.[[ParameterMap]]とする。
- isMappedを!
HasOwnProperty (map, P)とする。 - もしisMappedが
false なら、- ?
OrdinaryGet (args, P, Receiver)を返す。
- ?
- それ以外の場合、
10.4.4.4 [[Set]] ( P, V, Receiver )
- もし
SameValue (args, Receiver)がfalse なら、- isMappedを
false とする。
- isMappedを
- それ以外の場合、
- mapをargs.[[ParameterMap]]とする。
- isMappedを!
HasOwnProperty (map, P)とする。
- もしisMappedが
true なら、 - ?
OrdinarySet (args, P, V, Receiver)を返す。
10.4.4.5 [[Delete]] ( P )
- mapをargs.[[ParameterMap]]とする。
- isMappedを!
HasOwnProperty (map, P)とする。 - resultを?
OrdinaryDelete (args, P)とする。 - もしresultが
true かつisMappedがtrue なら、- ! map.[[Delete]](P)を実行する。
- resultを返す。
10.4.4.6 CreateUnmappedArgumentsObject ( argumentsList )
抽象操作CreateUnmappedArgumentsObjectは、引数argumentsList（
- lenをargumentsListの要素数とする。
- objを
OrdinaryObjectCreate (%Object.prototype% , « [[ParameterMap]] »)とする。 - obj.[[ParameterMap]]を
undefined に設定する。 - !
DefinePropertyOrThrow (obj,"length" , PropertyDescriptor { [[Value]]:𝔽 (len), [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:true }) を実行する。 - indexを0とする。
- 繰り返し、index
< lenの間、
- valをargumentsList[index]とする。
- !
CreateDataPropertyOrThrow (obj, !ToString (𝔽 (index)), val)を実行する。 - indexをindex + 1に設定する。
- !
DefinePropertyOrThrow (obj,%Symbol.iterator% , PropertyDescriptor { [[Value]]: %Array.prototype.values%, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:true }) を実行する。 - !
DefinePropertyOrThrow (obj,"callee" , PropertyDescriptor { [[Get]]:%ThrowTypeError% , [[Set]]:%ThrowTypeError% , [[Enumerable]]:false , [[Configurable]]:false }) を実行する。 - objを返す。
10.4.4.7 CreateMappedArgumentsObject ( func, formals, argumentsList, env )
抽象操作CreateMappedArgumentsObjectは、引数func（オブジェクト）、formals（
保証 ：formalsはrestパラメータ、バインディングパターン、初期化子を含まない。ただし重複識別子は許可される。- lenをargumentsListの要素数とする。
- objを
MakeBasicObject (« [[Prototype]], [[Extensible]], [[ParameterMap]] »)とする。 - obj.[[GetOwnProperty]]を
10.4.4.1 で規定されるものに設定する。 - obj.[[DefineOwnProperty]]を
10.4.4.2 で規定されるものに設定する。 - obj.[[Get]]を
10.4.4.3 で規定されるものに設定する。 - obj.[[Set]]を
10.4.4.4 で規定されるものに設定する。 - obj.[[Delete]]を
10.4.4.5 で規定されるものに設定する。 - obj.[[Prototype]]を
%Object.prototype% に設定する。 - mapを
OrdinaryObjectCreate (null )とする。 - obj.[[ParameterMap]]をmapに設定する。
- parameterNamesを
BoundNames of formalsとする。 - numberOfParametersをparameterNamesの要素数とする。
- indexを0とする。
- 繰り返し、index < lenの間、
- valをargumentsList[index]とする。
- !
CreateDataPropertyOrThrow (obj, !ToString (𝔽 (index)), val)を実行する。 - indexをindex + 1に設定する。
- !
DefinePropertyOrThrow (obj,"length" , PropertyDescriptor { [[Value]]:𝔽 (len), [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:true }) を実行する。 - mappedNamesを新しい空の
List とする。 - indexをnumberOfParameters - 1に設定する。
- 繰り返し、index ≥ 0の間、
- nameをparameterNames[index]とする。
- もしmappedNamesがnameを含まないなら、
- nameをmappedNamesに追加する。
- もしindex < lenなら、
- gを
MakeArgGetter (name, env)とする。 - pを
MakeArgSetter (name, env)とする。 - ! map.[[DefineOwnProperty]](!
ToString (𝔽 (index)), PropertyDescriptor { [[Set]]: p, [[Get]]: g, [[Enumerable]]:false , [[Configurable]]:true }) を実行する。
- gを
- indexをindex - 1に設定する。
- !
DefinePropertyOrThrow (obj,%Symbol.iterator% , PropertyDescriptor { [[Value]]: %Array.prototype.values%, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:true }) を実行する。 - !
DefinePropertyOrThrow (obj,"callee" , PropertyDescriptor { [[Value]]: func, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:true }) を実行する。 - objを返す。
10.4.4.7.1 MakeArgGetter ( name, env )
抽象操作MakeArgGetterは、引数name（文字列）、env（
- getterClosureを新しい
Abstract Closure （パラメータなし、nameとenvをキャプチャ）とし、呼び出されたとき次を行う：NormalCompletion (! env.GetBindingValue(name,false ))を返す。
- getterを
CreateBuiltinFunction (getterClosure, 0,"" , « »)とする。 - 注：getterはECMAScriptコードから直接アクセスされることはない。
- getterを返す。
10.4.4.7.2 MakeArgSetter ( name, env )
抽象操作MakeArgSetterは、引数name（文字列）、env（
- setterClosureを新しい
Abstract Closure （パラメータは(value)、nameとenvをキャプチャ）とし、呼び出されたとき次を行う：NormalCompletion (! env.SetMutableBinding(name, value,false ))を返す。
- setterを
CreateBuiltinFunction (setterClosure, 1,"" , « »)とする。 - 注：setterはECMAScriptコードから直接アクセスされることはない。
- setterを返す。
10.4.5 TypedArray エキゾチックオブジェクト
オブジェクトの[[PreventExtensions]]、[[GetOwnProperty]]、[[HasProperty]]、[[DefineOwnProperty]]、[[Get]]、[[Set]]、[[Delete]]、[[OwnPropertyKeys]]内部メソッドがこの節の定義を、その他の本質的内部メソッドが
10.4.5.1 [[PreventExtensions]] ( )
- 注：
6.1.7.3 で規定される拡張性関連の不変条件により、このメソッドは、Oがプロパティを増やしたり（あるいは失ってから再度増やしたり）できる場合（基礎バッファがリサイズされるときの整数インデックス名のプロパティなど）、true を返すことはできない。 - もし
IsTypedArrayFixedLength (O)がfalse なら、false を返す。 OrdinaryPreventExtensions (O)を返す。
10.4.5.2 [[GetOwnProperty]] ( P )
- もしPが
文字列 なら、- numericIndexを
CanonicalNumericIndexString (P)とする。 - もしnumericIndexが
undefined でなければ、- valueを
TypedArrayGetElement (O, numericIndex)とする。 - もしvalueが
undefined なら、undefined を返す。 - プロパティディスクリプタ { [[Value]]: value,
[[Writable]]:
true , [[Enumerable]]:true , [[Configurable]]:true } を返す。
- valueを
- numericIndexを
OrdinaryGetOwnProperty (O, P)を返す。
10.4.5.3 [[HasProperty]] ( P )
- もしPが
文字列 なら、- numericIndexを
CanonicalNumericIndexString (P)とする。 - もしnumericIndexが
undefined でなければ、IsValidIntegerIndex (O, numericIndex)を返す。
- numericIndexを
- ?
OrdinaryHasProperty (O, P)を返す。
10.4.5.4 [[DefineOwnProperty]] ( P, Desc )
- もしPが
文字列 なら、- numericIndexを
CanonicalNumericIndexString (P)とする。 - もしnumericIndexが
undefined でなければ、- もし
IsValidIntegerIndex (O, numericIndex)がfalse なら、false を返す。 - もしDescが[[Configurable]]フィールドを持ち、かつDesc.[[Configurable]]が
false なら、false を返す。 - もしDescが[[Enumerable]]フィールドを持ち、かつDesc.[[Enumerable]]が
false なら、false を返す。 - もし
IsAccessorDescriptor (Desc)がtrue なら、false を返す。 - もしDescが[[Writable]]フィールドを持ち、かつDesc.[[Writable]]が
false なら、false を返す。 - もしDescが[[Value]]フィールドを持つなら、?
TypedArraySetElement (O, numericIndex, Desc.[[Value]])を実行する。 true を返す。
- もし
- numericIndexを
- !
OrdinaryDefineOwnProperty (O, P, Desc)を返す。
10.4.5.5 [[Get]] ( P, Receiver )
- もしPが
文字列 なら、- numericIndexを
CanonicalNumericIndexString (P)とする。 - もしnumericIndexが
undefined でなければ、TypedArrayGetElement (O, numericIndex)を返す。
- numericIndexを
- ?
OrdinaryGet (O, P, Receiver)を返す。
10.4.5.6 [[Set]] ( P, V, Receiver )
- もしPが
文字列 なら、- numericIndexを
CanonicalNumericIndexString (P)とする。 - もしnumericIndexが
undefined でなければ、- もし
SameValue (O, Receiver)がtrue なら、- ?
TypedArraySetElement (O, numericIndex, V)を実行する。 true を返す。
- ?
- もし
IsValidIntegerIndex (O, numericIndex)がfalse なら、true を返す。
- もし
- numericIndexを
- ?
OrdinarySet (O, P, V, Receiver)を返す。
10.4.5.7 [[Delete]] ( P )
- もしPが
文字列 なら、- numericIndexを
CanonicalNumericIndexString (P)とする。 - もしnumericIndexが
undefined でなければ、- もし
IsValidIntegerIndex (O, numericIndex)がfalse ならtrue 、そうでなければfalse を返す。
- もし
- numericIndexを
- !
OrdinaryDelete (O, P)を返す。
10.4.5.8 [[OwnPropertyKeys]] ( )
- taRecordを
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst )とする。 - keysを新しい空の
List とする。 - もし
IsTypedArrayOutOfBounds (taRecord)がfalse なら、- lengthを
TypedArrayLength (taRecord)とする。 - 0 ≤ i < length となる各
整数 iについて、昇順で：
- lengthを
- Oの自身の
プロパティキー Pについて、Pが文字列 かつPが整数インデックス でないものを生成順に昇順で：- Pをkeysに追加する。
- Oの自身の
プロパティキー Pについて、Pがシンボル であるものを生成順に昇順で：- Pをkeysに追加する。
- keysを返す。
10.4.5.9 バッファ証人レコード付きTypedArray
バッファ証人レコード付きTypedArrayは、
バッファ証人レコード付きTypedArrayは、
| フィールド名 | 値 | 意味 |
|---|---|---|
| [[Object]] |
|
バッファのバイト長がロードされる |
| [[CachedBufferByteLength]] |
0以上の |
|
10.4.5.10 MakeTypedArrayWithBufferWitnessRecord ( obj, order )
抽象操作MakeTypedArrayWithBufferWitnessRecordは、引数obj（
- bufferをobj.[[ViewedArrayBuffer]]とする。
- もし
IsDetachedBuffer (buffer)がtrue なら、- byteLengthを
detached とする。
- byteLengthを
- それ以外の場合、
- byteLengthを
ArrayBufferByteLength (buffer, order)とする。
- byteLengthを
バッファ証人レコード付きTypedArray { [[Object]]: obj, [[CachedBufferByteLength]]: byteLength }を返す。
10.4.5.11 TypedArrayCreate ( prototype )
抽象操作TypedArrayCreateは、引数prototype（オブジェクト）を取り、
- internalSlotsListを« [[Prototype]], [[Extensible]], [[ViewedArrayBuffer]], [[TypedArrayName]], [[ContentType]], [[ByteLength]], [[ByteOffset]], [[ArrayLength]] »とする。
- Aを
MakeBasicObject (internalSlotsList)とする。 - A.[[PreventExtensions]]を
10.4.5.1 で規定されるものに設定する。 - A.[[GetOwnProperty]]を
10.4.5.2 で規定されるものに設定する。 - A.[[HasProperty]]を
10.4.5.3 で規定されるものに設定する。 - A.[[DefineOwnProperty]]を
10.4.5.4 で規定されるものに設定する。 - A.[[Get]]を
10.4.5.5 で規定されるものに設定する。 - A.[[Set]]を
10.4.5.6 で規定されるものに設定する。 - A.[[Delete]]を
10.4.5.7 で規定されるものに設定する。 - A.[[OwnPropertyKeys]]を
10.4.5.8 で規定されるものに設定する。 - A.[[Prototype]]をprototypeに設定する。
- Aを返す。
10.4.5.12 TypedArrayByteLength ( taRecord )
抽象操作TypedArrayByteLengthは、引数taRecord（
- もし
IsTypedArrayOutOfBounds (taRecord)がtrue なら、0を返す。 - lengthを
TypedArrayLength (taRecord)とする。 - もしlength = 0 なら、0を返す。
- OをtaRecord.[[Object]]とする。
- もしO.[[ByteLength]]が
auto でないなら、O.[[ByteLength]]を返す。 - elementSizeを
TypedArrayElementSize (O)とする。 - length × elementSizeを返す。
10.4.5.13 TypedArrayLength ( taRecord )
抽象操作TypedArrayLengthは、引数taRecord（
保証 ：IsTypedArrayOutOfBounds (taRecord)はfalse である。- OをtaRecord.[[Object]]とする。
- もしO.[[ArrayLength]]が
auto でないなら、O.[[ArrayLength]]を返す。 保証 ：IsFixedLengthArrayBuffer (O.[[ViewedArrayBuffer]])はfalse である。- byteOffsetをO.[[ByteOffset]]とする。
- elementSizeを
TypedArrayElementSize (O)とする。 - byteLengthをtaRecord.[[CachedBufferByteLength]]とする。
保証 ：byteLengthはdetached でない。floor ((byteLength - byteOffset) / elementSize)を返す。
10.4.5.14 IsTypedArrayOutOfBounds ( taRecord )
抽象操作IsTypedArrayOutOfBoundsは、引数taRecord（
- OをtaRecord.[[Object]]とする。
- bufferByteLengthをtaRecord.[[CachedBufferByteLength]]とする。
保証 ：IsDetachedBuffer (O.[[ViewedArrayBuffer]])がtrue となるのはbufferByteLengthがdetached のとき、かつそのときだけである。- もしbufferByteLengthが
detached なら、true を返す。 - byteOffsetStartをO.[[ByteOffset]]とする。
- もしO.[[ArrayLength]]が
auto なら、- byteOffsetEndをbufferByteLengthとする。
- それ以外の場合、
- elementSizeを
TypedArrayElementSize (O)とする。 - byteOffsetEndをbyteOffsetStart + O.[[ArrayLength]] × elementSizeとする。
- elementSizeを
- もしbyteOffsetStart > bufferByteLength または
byteOffsetEnd >
bufferByteLengthなら、
true を返す。 - 注：長さ0の
TypedArray は範囲外とはみなされない。 false を返す。
10.4.5.15 IsTypedArrayFixedLength ( O )
抽象操作IsTypedArrayFixedLengthは、引数O（
- もしO.[[ArrayLength]]が
auto なら、false を返す。 - bufferをO.[[ViewedArrayBuffer]]とする。
- もし
IsFixedLengthArrayBuffer (buffer)がfalse かつIsSharedArrayBuffer (buffer)がfalse なら、false を返す。 true を返す。
10.4.5.16 IsValidIntegerIndex ( O, index )
抽象操作IsValidIntegerIndexは、引数O（
- もし
IsDetachedBuffer (O.[[ViewedArrayBuffer]])がtrue なら、false を返す。 - もしindexが
整数値(Number) でなければ、false を返す。 - もしindexが
-0 𝔽またはindex <-0 𝔽なら、false を返す。 - taRecordを
MakeTypedArrayWithBufferWitnessRecord (O,unordered )とする。 - 注：バッファが拡張可能なSharedArrayBufferの場合、境界チェックは同期化操作ではない。
- もし
IsTypedArrayOutOfBounds (taRecord)がtrue なら、false を返す。 - lengthを
TypedArrayLength (taRecord)とする。 - もし
ℝ (index) ≥ lengthなら、false を返す。 true を返す。
10.4.5.17 TypedArrayGetElement ( O, index )
抽象操作TypedArrayGetElementは、引数O（
- もし
IsValidIntegerIndex (O, index)がfalse なら、undefined を返す。 - offsetをO.[[ByteOffset]]とする。
- elementSizeを
TypedArrayElementSize (O)とする。 - byteIndexInBufferを(
ℝ (index) × elementSize) + offsetとする。 - elementTypeを
TypedArrayElementType (O)とする。 GetValueFromBuffer (O.[[ViewedArrayBuffer]], byteIndexInBuffer, elementType,true ,unordered )を返す。
10.4.5.18 TypedArraySetElement ( O, index, value )
抽象操作 TypedArraySetElement は、引数 O（
- もし O.[[ContentType]] が
bigint なら、numValue に ?ToBigInt (value) を設定する。 - それ以外の場合、numValue に ?
ToNumber (value) を設定する。 IsValidIntegerIndex (O, index) がtrue なら、- offset に O.[[ByteOffset]] を設定する。
- elementSize に
TypedArrayElementSize (O) を設定する。 - byteIndexInBuffer に (
ℝ (index) × elementSize) + offset を設定する。 - elementType に
TypedArrayElementType (O) を設定する。 SetValueInBuffer (O.[[ViewedArrayBuffer]], byteIndexInBuffer, elementType, numValue,true ,unordered ) を実行する。
unused を返す。
この操作は常に成功したように見えるが、
10.4.5.19 IsArrayBufferViewOutOfBounds ( O )
抽象操作 IsArrayBufferViewOutOfBounds は、引数 O（
- もし O が [[DataView]] 内部スロットを持つなら、
- viewRecord に
MakeDataViewWithBufferWitnessRecord (O,seq-cst ) を設定する。 IsViewOutOfBounds (viewRecord) を返す。
- viewRecord に
- taRecord に
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ) を設定する。 IsTypedArrayOutOfBounds (taRecord) を返す。
10.4.6 モジュール名前空間エキゾチックオブジェクト
export *
によって間接的にエクスポートされたバインディングも含まれる。それぞれの String 値の own
あるオブジェクトが モジュール名前空間エキゾチックオブジェクト であるとは、その [[GetPrototypeOf]]、[[SetPrototypeOf]]、[[IsExtensible]]、[[PreventExtensions]]、[[GetOwnProperty]]、[[DefineOwnProperty]]、[[HasProperty]]、[[Get]]、[[Set]]、[[Delete]]、[[OwnPropertyKeys]] 内部メソッドが本節の定義を使用し、それ以外の本質的な内部メソッドが
| 内部スロット | 型 | 説明 |
|---|---|---|
| [[Module]] |
|
この名前空間が公開するエクスポートを持つ |
| [[Exports]] |
|
このオブジェクトの own プロパティとして公開されているエクスポート名の String 値の |
10.4.6.1 [[GetPrototypeOf]] ( )
null を返す。
10.4.6.2 [[SetPrototypeOf]] ( V )
- !
SetImmutablePrototype (O, V) を返す。
10.4.6.3 [[IsExtensible]] ( )
false を返す。
10.4.6.4 [[PreventExtensions]] ( )
true を返す。
10.4.6.5 [[GetOwnProperty]] ( P )
- もし P が
Symbol である 場合、OrdinaryGetOwnProperty (O, P) を返す。 - exports を O.[[Exports]] とする。
- もし exports が P を含まない場合、
undefined を返す。 - value を ? O.[[Get]](P, O) とする。
- PropertyDescriptor { [[Value]]: value,
[[Writable]]:
true , [[Enumerable]]:true , [[Configurable]]:false } を返す。
10.4.6.6 [[DefineOwnProperty]] ( P, Desc )
- もし P が
Symbol である 場合、!OrdinaryDefineOwnProperty (O, P, Desc) を返す。 - current を ? O.[[GetOwnProperty]](P) とする。
- もし current が
undefined なら、false を返す。 - もし Desc が [[Configurable]] フィールドを持ち、かつ
Desc.[[Configurable]] が
true である場合、false を返す。 - もし Desc が [[Enumerable]] フィールドを持ち、かつ
Desc.[[Enumerable]] が
false である場合、false を返す。 - もし
IsAccessorDescriptor (Desc) がtrue なら、false を返す。 - もし Desc が [[Writable]] フィールドを持ち、かつ
Desc.[[Writable]] が
false である場合、false を返す。 - もし Desc が [[Value]] フィールドを持つなら、
SameValue (Desc.[[Value]], current.[[Value]]) を返す。 true を返す。
10.4.6.7 [[HasProperty]] ( P )
- もし P が
Symbol である 場合、!OrdinaryHasProperty (O, P) を返す。 - exports を O.[[Exports]] とする。
- もし exports が P を含む場合、
true を返す。 false を返す。
10.4.6.8 [[Get]] ( P, Receiver )
- もし P が
Symbol である 場合、- !
OrdinaryGet (O, P, Receiver) を返す。
- !
- exports を O.[[Exports]] とする。
- もし exports が P を含まない場合、
undefined を返す。 - m を O.[[Module]] とする。
- binding を m.ResolveExport(P) とする。
アサート ： binding はResolvedBinding レコード である。- targetModule を binding.[[Module]] とする。
アサート ： targetModule はundefined ではない。- もし binding.[[BindingName]] が
namespace である場合、GetModuleNamespace (targetModule) を返す。
- targetEnv を targetModule.[[Environment]] とする。
- もし targetEnv が
empty である場合、ReferenceError 例外をスローする。 - ? targetEnv.GetBindingValue(binding.[[BindingName]],
true ) を返す。
ResolveExport は副作用を持たない。この操作が特定の exportName・resolveSet
の組み合わせで呼ばれるたびに、常に同じ結果を返さなければならない。実装は各 [[Exports]] に対して
ResolveExport の結果を事前計算・キャッシュしてもよい。
10.4.6.9 [[Set]] ( P, V, Receiver )
false を返す。
10.4.6.10 [[Delete]] ( P )
- もし P が
Symbol である 場合、- !
OrdinaryDelete (O, P) を返す。
- !
- exports を O.[[Exports]] とする。
- もし exports が P を含む場合、
false を返す。 true を返す。
10.4.6.11 [[OwnPropertyKeys]] ( )
- exports を O.[[Exports]] とする。
- symbolKeys を
OrdinaryOwnPropertyKeys (O) とする。 リスト連結 により exports と symbolKeys を結合したリストを返す。
10.4.6.12 ModuleNamespaceCreate ( module, exports )
抽象操作 ModuleNamespaceCreate は、引数 module（
アサート ： module.[[Namespace]] はempty である。- internalSlotsList を
表 33 に記載されている内部スロットとする。 - M を
MakeBasicObject (internalSlotsList) とする。 - M の本質的な内部メソッドを
10.4.6 で指定された定義に設定する。 - M.[[Module]] に module を設定する。
- sortedExports を
リスト （要素は exports の要素を辞書式コードユニット順 にソートしたもの）とする。 - M.[[Exports]] に sortedExports を設定する。
- M の own プロパティを
28.3 の定義に対応して作成する。 - module.[[Namespace]] に M を設定する。
- M を返す。
10.4.7 不変プロトタイプエキゾチックオブジェクト
あるオブジェクトが 不変プロトタイプエキゾチックオブジェクト
であるとは、その [[SetPrototypeOf]] 内部メソッドが以下の実装を用いる場合である（その他の本質的な内部メソッドは、対象の
他の
10.4.7.1 [[SetPrototypeOf]] ( V )
- ?
SetImmutablePrototype (O, V) を返す。
10.4.7.2 SetImmutablePrototype ( O, V )
抽象操作 SetImmutablePrototype は、引数 O（Object）、V（Object または
- current を ? O.[[GetPrototypeOf]]() とする。
SameValue (V, current) がtrue なら、true を返す。false を返す。
10.5 Proxy オブジェクトの内部メソッドおよび内部スロット
Proxy オブジェクトは、
あるオブジェクトが Proxy
エキゾチックオブジェクト であるとは、その本質的な内部メソッド（該当する場合は [[Call]] および [[Construct]] を含む）が本節の定義を使う場合である。これらの内部メソッドは
| 内部メソッド | ハンドラーメソッド |
|---|---|
| [[GetPrototypeOf]] |
getPrototypeOf
|
| [[SetPrototypeOf]] |
setPrototypeOf
|
| [[IsExtensible]] |
isExtensible
|
| [[PreventExtensions]] |
preventExtensions
|
| [[GetOwnProperty]] |
getOwnPropertyDescriptor
|
| [[DefineOwnProperty]] |
defineProperty
|
| [[HasProperty]] |
has
|
| [[Get]] |
get
|
| [[Set]] |
set
|
| [[Delete]] |
deleteProperty
|
| [[OwnPropertyKeys]] |
ownKeys
|
| [[Call]] |
apply
|
| [[Construct]] |
construct
|
ハンドラーメソッドが Proxy オブジェクト内部メソッドの実装として呼び出されるとき、そのハンドラーメソッドにはプロキシのターゲットオブジェクトがパラメータとして渡される。プロキシのハンドラーオブジェクトは必ずしもすべての本質的な内部メソッドに対応するメソッドを持つ必要はない。プロキシ上で内部メソッドが呼ばれた際に、ハンドラーオブジェクトが該当するトラップメソッドを持たない場合は、プロキシのターゲットオブジェクト上の対応する内部メソッドが呼び出される。
Proxy オブジェクトの [[ProxyHandler]] および [[ProxyTarget]]
内部スロットは、オブジェクト生成時に常に初期化され、通常は変更されない。一部の Proxy
オブジェクトは、生成後にrevoke（無効化）できるような方法で作成される。プロキシが無効化されると、その [[ProxyHandler]] および [[ProxyTarget]] 内部スロットは
Proxy オブジェクトは本質的な内部メソッドの実装を任意の ECMAScript コードで提供可能であるため、ハンドラーメソッドが
以下のアルゴリズム記述では、O は ECMAScript Proxy オブジェクト、P は
10.5.1 [[GetPrototypeOf]] ( )
- ?
ValidateNonRevokedProxy (O) を実行する。 - target を O.[[ProxyTarget]] とする。
- handler を O.[[ProxyHandler]] とする。
アサート ：handler はObject である 。- trap を ?
GetMethod (handler,"getPrototypeOf" ) とする。 - もし trap が
undefined なら、- ? target.[[GetPrototypeOf]]() を返す。
- handlerProto を ?
Call (trap, handler, « target » ) とする。 - もし handlerProto が
Object でない かつ handlerProto がnull でない場合、TypeError 例外をスローする。 - extensibleTarget を ?
IsExtensible (target) とする。 - もし extensibleTarget が
true なら、handlerProto を返す。 - targetProto を ? target.[[GetPrototypeOf]]() とする。
- もし
SameValue (handlerProto, targetProto) がfalse なら、TypeError 例外をスローする。 - handlerProto を返す。
Proxy オブジェクトの [[GetPrototypeOf]] は以下の不変条件を強制する：
-
[[GetPrototypeOf]] の結果は Object または
null でなければならない。 - ターゲットオブジェクトが拡張不可能な場合、Proxy オブジェクトに対する [[GetPrototypeOf]] は、ターゲットオブジェクトに対する [[GetPrototypeOf]] と同じ値を返さなければならない。
10.5.2 [[SetPrototypeOf]] ( V )
- ?
ValidateNonRevokedProxy (O) を実行する。 - target を O.[[ProxyTarget]] とする。
- handler を O.[[ProxyHandler]] とする。
アサート ：handler はObject である 。- trap を ?
GetMethod (handler,"setPrototypeOf" ) とする。 - もし trap が
undefined なら、- ? target.[[SetPrototypeOf]](V) を返す。
- booleanTrapResult を
ToBoolean (?Call (trap, handler, « target, V »)) とする。 - もし booleanTrapResult が
false なら、false を返す。 - extensibleTarget を ?
IsExtensible (target) とする。 - もし extensibleTarget が
true なら、true を返す。 - targetProto を ? target.[[GetPrototypeOf]]() とする。
- もし
SameValue (V, targetProto) がfalse なら、TypeError 例外をスローする。 true を返す。
Proxy オブジェクトの [[SetPrototypeOf]] は以下の不変条件を強制する：
-
[[SetPrototypeOf]] の結果は
Boolean 値である。 - ターゲットオブジェクトが拡張不可能な場合、引数の値はターゲットオブジェクトに対する [[GetPrototypeOf]] の結果と同じでなければならない。
10.5.3 [[IsExtensible]] ( )
- ?
ValidateNonRevokedProxy (O) を実行する。 - target を O.[[ProxyTarget]] とする。
- handler を O.[[ProxyHandler]] とする。
アサート ：handler はObject である 。- trap を ?
GetMethod (handler,"isExtensible" ) とする。 - もし trap が
undefined なら、- ?
IsExtensible (target) を返す。
- ?
- booleanTrapResult を
ToBoolean (?Call (trap, handler, « target » )) とする。 - targetResult を ?
IsExtensible (target) とする。 - もし booleanTrapResult が targetResult
と異なる場合、
TypeError 例外をスローする。 - booleanTrapResult を返す。
Proxy オブジェクトの [[IsExtensible]] は以下の不変条件を強制する：
-
[[IsExtensible]] の結果は
Boolean 値である。 - Proxy オブジェクトに対して [[IsExtensible]] を適用した結果は、同じ引数でターゲットオブジェクトに [[IsExtensible]] を適用した結果と同じでなければならない。
10.5.4 [[PreventExtensions]] ( )
- ?
ValidateNonRevokedProxy (O) を実行する。 - target を O.[[ProxyTarget]] とする。
- handler を O.[[ProxyHandler]] とする。
アサート ：handler はObject である 。- trap を ?
GetMethod (handler,"preventExtensions" ) とする。 - もし trap が
undefined なら、- ? target.[[PreventExtensions]]() を返す。
- booleanTrapResult を
ToBoolean (?Call (trap, handler, « target » )) とする。 - もし booleanTrapResult が
true なら、- extensibleTarget を ?
IsExtensible (target) とする。 - もし extensibleTarget が
true なら、TypeError 例外をスローする。
- extensibleTarget を ?
- booleanTrapResult を返す。
Proxy オブジェクトの [[PreventExtensions]] は以下の不変条件を強制する：
-
[[PreventExtensions]] の結果は
Boolean 値である。 -
Proxy オブジェクトに対して [[PreventExtensions]] を適用した結果が
true となるのは、ターゲットオブジェクトに対する [[IsExtensible]] の結果がfalse の場合のみである。
10.5.5 [[GetOwnProperty]] ( P )
- ?
ValidateNonRevokedProxy (O) を実行する。 - target を O.[[ProxyTarget]] とする。
- handler を O.[[ProxyHandler]] とする。
アサート : handler はObject である 。- trap を ?
GetMethod (handler,"getOwnPropertyDescriptor" ) とする。 - もし trap が
undefined なら、- ? target.[[GetOwnProperty]](P) を返す。
- trapResultObj を ?
Call (trap, handler, « target, P » ) とする。 - もし trapResultObj が
Object でない かつ trapResultObj がundefined でない場合、TypeError 例外をスローする。 - targetDesc を ? target.[[GetOwnProperty]](P) とする。
- もし trapResultObj が
undefined なら、- もし targetDesc が
undefined なら、undefined を返す。 - もし targetDesc.[[Configurable]] が
false なら、TypeError 例外をスローする。 - extensibleTarget を ?
IsExtensible (target) とする。 - もし extensibleTarget が
false なら、TypeError 例外をスローする。 undefined を返す。
- もし targetDesc が
- extensibleTarget を ?
IsExtensible (target) とする。 - resultDesc を ?
ToPropertyDescriptor (trapResultObj) とする。 CompletePropertyDescriptor (resultDesc) を実行する。- valid を
IsCompatiblePropertyDescriptor (extensibleTarget, resultDesc, targetDesc) とする。 - もし valid が
false なら、TypeError 例外をスローする。 - もし resultDesc.[[Configurable]] が
false なら、- もし targetDesc が
undefined または targetDesc.[[Configurable]] がtrue なら、TypeError 例外をスローする。
- もし resultDesc が [[Writable]] フィールドを持ち、かつ
resultDesc.[[Writable]] が
false なら、アサート : targetDesc は [[Writable]] フィールドを持つ。- もし targetDesc.[[Writable]] が
true なら、TypeError 例外をスローする。
- もし targetDesc が
- resultDesc を返す。
Proxy オブジェクトの [[GetOwnProperty]] は以下の不変条件を強制する：
-
[[GetOwnProperty]] の結果は Object または
undefined でなければならない。 - ターゲットオブジェクトの non-configurable な own プロパティが存在する場合、そのプロパティは存在しないと報告できない。
- ターゲットオブジェクトに own プロパティが存在し、かつターゲットオブジェクトが拡張不可能な場合、そのプロパティは存在しないと報告できない。
- ターゲットオブジェクトに own プロパティが存在しない、かつターゲットオブジェクトが拡張不可能な場合、そのプロパティは存在すると報告できない。
- non-configurable として報告できるのは、ターゲットオブジェクトの non-configurable な own プロパティが存在する場合のみである。
- non-configurable かつ non-writable として報告できるのは、ターゲットオブジェクトに non-configurable かつ non-writable な own プロパティが存在する場合のみである。
10.5.6 [[DefineOwnProperty]] ( P, Desc )
- ?
ValidateNonRevokedProxy (O) を実行する。 - target を O.[[ProxyTarget]] とする。
- handler を O.[[ProxyHandler]] とする。
アサート : handler はObject である 。- trap を ?
GetMethod (handler,"defineProperty" ) とする。 - もし trap が
undefined なら、- ? target.[[DefineOwnProperty]](P, Desc) を返す。
- descObj を
FromPropertyDescriptor (Desc) とする。 - booleanTrapResult を
ToBoolean (?Call (trap, handler, « target, P, descObj »)) とする。 - もし booleanTrapResult が
false なら、false を返す。 - targetDesc を ? target.[[GetOwnProperty]](P) とする。
- extensibleTarget を ?
IsExtensible (target) とする。 - もし Desc が [[Configurable]] フィールドを持ち、かつ
Desc.[[Configurable]] が
false なら、- settingConfigFalse を
true とする。
- settingConfigFalse を
- それ以外の場合、
- settingConfigFalse を
false とする。
- settingConfigFalse を
- もし targetDesc が
undefined なら、- もし extensibleTarget が
false なら、TypeError 例外をスローする。 - もし settingConfigFalse が
true なら、TypeError 例外をスローする。
- もし extensibleTarget が
- それ以外の場合、
- もし
IsCompatiblePropertyDescriptor (extensibleTarget, Desc, targetDesc) がfalse なら、TypeError 例外をスローする。 - もし settingConfigFalse が
true かつ targetDesc.[[Configurable]] がtrue なら、TypeError 例外をスローする。 - もし
IsDataDescriptor (targetDesc) がtrue かつ targetDesc.[[Configurable]] がfalse かつ targetDesc.[[Writable]] がtrue なら、- もし Desc が [[Writable]] フィールドを持ち、かつ
Desc.[[Writable]] が
false なら、TypeError 例外をスローする。
- もし Desc が [[Writable]] フィールドを持ち、かつ
Desc.[[Writable]] が
- もし
true を返す。
Proxy オブジェクトの [[DefineOwnProperty]] は以下の不変条件を強制する：
-
[[DefineOwnProperty]] の結果は
Boolean 値である。 - ターゲットオブジェクトが拡張不可能な場合、プロパティを追加できない。
- non-configurable にできるのは、対応する non-configurable なターゲットオブジェクトの own プロパティが存在する場合のみ。
- non-configurable かつ non-writable にできるのは、対応する non-configurable かつ non-writable なターゲットオブジェクトの own プロパティが存在する場合のみ。
- プロパティに対応するターゲットオブジェクトのプロパティが存在する場合、そのプロパティディスクリプタをターゲットオブジェクトに [[DefineOwnProperty]] で適用しても例外は発生しない。
10.5.7 [[HasProperty]] ( P )
- ?
ValidateNonRevokedProxy (O) を実行する。 - target を O.[[ProxyTarget]] とする。
- handler を O.[[ProxyHandler]] とする。
アサート : handler はObject である 。- trap を ?
GetMethod (handler,"has" ) とする。 - もし trap が
undefined なら、- ? target.[[HasProperty]](P) を返す。
- booleanTrapResult を
ToBoolean (?Call (trap, handler, « target, P » )) とする。 - もし booleanTrapResult が
false なら、- targetDesc を ? target.[[GetOwnProperty]](P) とする。
- もし targetDesc が
undefined でなければ、- もし targetDesc.[[Configurable]] が
false なら、TypeError 例外をスローする。 - extensibleTarget を ?
IsExtensible (target) とする。 - もし extensibleTarget が
false なら、TypeError 例外をスローする。
- もし targetDesc.[[Configurable]] が
- booleanTrapResult を返す。
Proxy オブジェクトの [[HasProperty]] は以下の不変条件を強制する：
-
[[HasProperty]] の結果は
Boolean 値である。 - ターゲットオブジェクトの non-configurable な own プロパティが存在する場合、そのプロパティは存在しないと報告できない。
- ターゲットオブジェクトに own プロパティが存在し、かつターゲットオブジェクトが拡張不可能な場合、そのプロパティは存在しないと報告できない。
10.5.8 [[Get]] ( P, Receiver )
- ?
ValidateNonRevokedProxy (O) を実行する。 - target を O.[[ProxyTarget]] とする。
- handler を O.[[ProxyHandler]] とする。
アサート : handler はObject である 。- trap を ?
GetMethod (handler,"get" ) とする。 - もし trap が
undefined なら、- ? target.[[Get]](P, Receiver) を返す。
- trapResult を ?
Call (trap, handler, « target, P, Receiver » ) とする。 - targetDesc を ? target.[[GetOwnProperty]](P) とする。
- もし targetDesc が
undefined でなく、かつ targetDesc.[[Configurable]] がfalse なら、- もし
IsDataDescriptor (targetDesc) がtrue かつ targetDesc.[[Writable]] がfalse なら、- もし
SameValue (trapResult, targetDesc.[[Value]]) がfalse なら、TypeError 例外をスローする。
- もし
- もし
IsAccessorDescriptor (targetDesc) がtrue かつ targetDesc.[[Get]] がundefined なら、- もし trapResult が
undefined でない場合、TypeError 例外をスローする。
- もし trapResult が
- もし
- trapResult を返す。
10.5.9 [[Set]] ( P, V, Receiver )
- ?
ValidateNonRevokedProxy (O) を実行する。 - target を O.[[ProxyTarget]] とする。
- handler を O.[[ProxyHandler]] とする。
アサート : handler はObject である 。- trap を ?
GetMethod (handler,"set" ) とする。 - もし trap が
undefined なら、- ? target.[[Set]](P, V, Receiver) を返す。
- booleanTrapResult を
ToBoolean (?Call (trap, handler, « target, P, V, Receiver »)) とする。 - もし booleanTrapResult が
false なら、false を返す。 - targetDesc を ? target.[[GetOwnProperty]](P) とする。
- もし targetDesc が
undefined でなく、 targetDesc.[[Configurable]] がfalse なら、- もし
IsDataDescriptor (targetDesc) がtrue かつ targetDesc.[[Writable]] がfalse なら、SameValue (V, targetDesc.[[Value]]) がfalse なら、TypeError 例外をスローする。
- もし
IsAccessorDescriptor (targetDesc) がtrue なら、- もし targetDesc.[[Set]] が
undefined なら、TypeError 例外をスローする。
- もし targetDesc.[[Set]] が
- もし
true を返す。
10.5.10 [[Delete]] ( P )
- ?
ValidateNonRevokedProxy (O) を実行する。 - target を O.[[ProxyTarget]] とする。
- handler を O.[[ProxyHandler]] とする。
アサート : handler はObject である 。- trap を ?
GetMethod (handler,"deleteProperty" ) とする。 - もし trap が
undefined なら、- ? target.[[Delete]](P) を返す。
- booleanTrapResult を
ToBoolean (?Call (trap, handler, « target, P »)) とする。 - もし booleanTrapResult が
false なら、false を返す。 - targetDesc を ? target.[[GetOwnProperty]](P) とする。
- もし targetDesc が
undefined なら、true を返す。 - もし targetDesc.[[Configurable]] が
false なら、TypeError 例外をスローする。 - extensibleTarget を ?
IsExtensible (target) とする。 - もし extensibleTarget が
false なら、TypeError 例外をスローする。 true を返す。
Proxy オブジェクトの [[Delete]] は次の不変条件を強制する：
-
[[Delete]] の結果は
Boolean 値である。 - 対象プロパティがターゲットオブジェクトの非設定可能 own プロパティである場合、それを削除済みとして報告することはできない。
- 対象プロパティがターゲットオブジェクトの own プロパティであり、ターゲットオブジェクトが拡張不可能な場合、それを削除済みとして報告することはできない。
10.5.11 [[OwnPropertyKeys]] ( )
- ?
ValidateNonRevokedProxy (O) を実行する。 - target を O.[[ProxyTarget]] とする。
- handler を O.[[ProxyHandler]] とする。
アサート : handler はObject である 。- trap を ?
GetMethod (handler,"ownKeys" ) とする。 - もし trap が
undefined なら、- ? target.[[OwnPropertyKeys]]() を返す。
- trapResultArray を ?
Call (trap, handler, « target » ) とする。 - trapResult を ?
CreateListFromArrayLike (trapResultArray,property-key ) とする。 - もし trapResult に重複する要素が含まれていた場合、
TypeError 例外をスローする。 - extensibleTarget を ?
IsExtensible (target) とする。 - targetKeys を ? target.[[OwnPropertyKeys]]() とする。
アサート : targetKeys はリスト （プロパティキー ）である。アサート : targetKeys には重複する要素は含まれていない。- targetConfigurableKeys を新しい空の
リスト とする。 - targetNonconfigurableKeys を新しい空の
リスト とする。 - targetKeys の各要素 key について、
- desc を ? target.[[GetOwnProperty]](key) とする。
- もし desc が
undefined でなく、desc.[[Configurable]] がfalse なら、- key を targetNonconfigurableKeys に追加する。
- それ以外の場合、
- key を targetConfigurableKeys に追加する。
- もし extensibleTarget が
true かつ targetNonconfigurableKeys が空であるなら、- trapResult を返す。
- uncheckedResultKeys を
リスト （要素は trapResult の要素）とする。 - targetNonconfigurableKeys の各要素 key について、
- もし uncheckedResultKeys に key
が含まれなければ、
TypeError 例外をスローする。 - key を uncheckedResultKeys から削除する。
- もし uncheckedResultKeys に key
が含まれなければ、
- もし extensibleTarget が
true なら、trapResult を返す。 - targetConfigurableKeys の各要素 key について、
- もし uncheckedResultKeys に key
が含まれなければ、
TypeError 例外をスローする。 - key を uncheckedResultKeys から削除する。
- もし uncheckedResultKeys に key
が含まれなければ、
- もし uncheckedResultKeys が空でない場合、
TypeError 例外をスローする。 - trapResult を返す。
10.5.12 [[Call]] ( thisArgument, argumentsList )
- ?
ValidateNonRevokedProxy (O) を実行する。 - target を O.[[ProxyTarget]] とする。
- handler を O.[[ProxyHandler]] とする。
アサート : handler はObject である 。- trap を ?
GetMethod (handler,"apply" ) とする。 - もし trap が
undefined なら、- ?
Call (target, thisArgument, argumentsList) を返す。
- ?
- argArray を
CreateArrayFromList (argumentsList) とする。 - ?
Call (trap, handler, « target, thisArgument, argArray » ) を返す。
10.5.13 [[Construct]] ( argumentsList, newTarget )
- ?
ValidateNonRevokedProxy (O) を実行する。 - target を O.[[ProxyTarget]] とする。
アサート :IsConstructor (target) はtrue である。- handler を O.[[ProxyHandler]] とする。
アサート : handler はObject である 。- trap を ?
GetMethod (handler,"construct" ) とする。 - もし trap が
undefined なら、- ?
Construct (target, argumentsList, newTarget) を返す。
- ?
- argArray を
CreateArrayFromList (argumentsList) とする。 - newObj を ?
Call (trap, handler, « target, argArray, newTarget » ) とする。 - もし newObj が
Object でない 場合、TypeError 例外をスローする。 - newObj を返す。
Proxy オブジェクトの [[Construct]] は次の不変条件を強制する：
- [[Construct]] の結果は Object でなければならない。
10.5.14 ValidateNonRevokedProxy ( proxy )
抽象操作 ValidateNonRevokedProxy は、引数 proxy（
- もし proxy.[[ProxyTarget]] が
null なら、TypeError 例外をスローする。 アサート ： proxy.[[ProxyHandler]] はnull ではない。unused を返す。
10.5.15 ProxyCreate ( target, handler )
抽象操作 ProxyCreate は、引数 target（
- もし target が
Object でない 場合、TypeError 例外をスローする。 - もし handler が
Object でない 場合、TypeError 例外をスローする。 - P を
MakeBasicObject (« [[ProxyHandler]], [[ProxyTarget]] ») とする。 - P の本質的な内部メソッド（[[Call]] および [[Construct]] を除く）を、
10.5 で指定された定義に設定する。 - もし
IsCallable (target) がtrue なら、- P.[[Call]] を
10.5.12 で指定されたとおりに設定する。 - もし
IsConstructor (target) がtrue なら、- P.[[Construct]] を
10.5.13 で指定されたとおりに設定する。
- P.[[Construct]] を
- P.[[Call]] を
- P.[[ProxyTarget]] に target を設定する。
- P.[[ProxyHandler]] に handler を設定する。
- P を返す。
11 ECMAScript 言語：ソーステキスト
11.1 ソーステキスト
構文
ECMAScript ソーステキストは、Unicode コードポイントの列である。U+0000 から U+10FFFF までのすべての Unicode
コードポイント値（サロゲートコードポイントを含む）は、ECMAScript 文法で許可される場所で ECMAScript ソーステキスト内に出現できる。ECMAScript
ソーステキストを保存・交換する際に用いられる実際のエンコーディングは本仕様に関係しない。外部ソーステキストのエンコーディングに関わらず、適合 ECMAScript 実装は、ソーステキストを等価な
結合文字列の構成要素は、ユーザーが全体を 1 文字と考える場合でも、個々の Unicode コードポイントとして扱われる。
文字列リテラル、正規表現リテラル、テンプレートリテラル、識別子では、任意の Unicode コードポイントも、その数値値を明示的に表す Unicode エスケープシーケンスで表すことができる。コメント内では、このようなエスケープシーケンスはコメントの一部として事実上無視される。
ECMAScript は、Unicode エスケープシーケンスの振る舞いが Java プログラミング言語と異なる。たとえば Java プログラム内で
\u000A のようなエスケープシーケンスが単一行コメント内に現れると、それは行終端子（Unicode コードポイント U+000A：LINE FEED
(LF)）として解釈され、次のコードポイントはコメントの一部とならない。同様に、Java プログラムの文字列リテラル内で \u000A
が現れると、それも行終端子と解釈され、文字列リテラル内に行終端子を含めることはできない。LINE FEED (LF) を文字列リテラルの値の一部にしたい場合は
\n を使う必要がある。ECMAScript プログラムでは、コメント内の Unicode
エスケープシーケンスは決して解釈されず、コメントの終了に寄与することはない。同様に、ECMAScript プログラム内の文字列リテラル内で発生する Unicode
エスケープシーケンスは常にリテラルの一部となり、行終端子や文字列リテラルの終了となるコードポイントとして解釈されることはない。
11.1.1 静的セマンティクス: UTF16EncodeCodePoint ( cp )
抽象操作 UTF16EncodeCodePoint は、引数 cp（Unicode コードポイント）を取り、文字列を返す。呼び出されたとき、次の手順を実行する：
11.1.2 静的セマンティクス: CodePointsToString ( text )
抽象操作 CodePointsToString は、引数 text（Unicode コードポイント列）を取り、文字列を返す。text を
- result を空文字列とする。
- text の各コードポイント cp について、
- result を result と
UTF16EncodeCodePoint (cp) の文字列連結 に設定する。
- result を result と
- result を返す。
11.1.3 静的セマンティクス: UTF16SurrogatePairToCodePoint ( lead, trail )
抽象操作 UTF16SurrogatePairToCodePoint は、引数
lead（コードユニット）、trail（コードユニット）を取り、コードポイントを返す。UTF-16
アサート : lead はリーディングサロゲート であり、trail はトレーリングサロゲート である。- cp を (lead - 0xD800) × 0x400 + (trail - 0xDC00) + 0x10000 とする。
- コードポイント cp を返す。
11.1.4 静的セマンティクス: CodePointAt ( string, position )
抽象操作 CodePointAt は、引数 string（文字列）、position（非負の
- size を string の長さとする。
アサート : position ≥ 0 かつ position < size。- first を string の position 番目のコードユニットとする。
- cp を first の数値値を持つコードポイントとする。
- もし first が
リーディングサロゲート でもトレーリングサロゲート でもない場合、Record { [[CodePoint]]: cp, [[CodeUnitCount]]: 1, [[IsUnpairedSurrogate]]:false } を返す。
- もし first が
トレーリングサロゲート であるか、position + 1 = size なら、Record { [[CodePoint]]: cp, [[CodeUnitCount]]: 1, [[IsUnpairedSurrogate]]:true } を返す。
- second を string の position + 1 番目のコードユニットとする。
- もし second が
トレーリングサロゲート でない場合、Record { [[CodePoint]]: cp, [[CodeUnitCount]]: 1, [[IsUnpairedSurrogate]]:true } を返す。
- cp を
UTF16SurrogatePairToCodePoint (first, second) に設定する。 Record { [[CodePoint]]: cp, [[CodeUnitCount]]: 2, [[IsUnpairedSurrogate]]:false } を返す。
11.1.5 静的セマンティクス: StringToCodePoints ( string )
抽象操作 StringToCodePoints は、引数 string（文字列）を取り、
- codePoints を新しい空の
リスト とする。 - size を string の長さとする。
- position を 0 とする。
- position < size の間、繰り返す：
- cp を
CodePointAt (string, position) に設定する。 - cp.[[CodePoint]] を codePoints に追加する。
- position を position + cp.[[CodeUnitCount]] に設定する。
- cp を
- codePoints を返す。
11.1.6 静的セマンティクス: ParseText ( sourceText, goalSymbol )
抽象操作 ParseText は、引数 sourceText（文字列または Unicode
コードポイント列）、goalSymbol（ECMAScript 文法の非終端記号）を取り、
- もし sourceText が
文字列 なら、sourceText をStringToCodePoints (sourceText) に設定する。 - sourceText を goalSymbol を
ゴール記号 として用いて構文解析し、パース結果についてearly error 条件を解析する。構文解析およびearly error 検出は、実装定義 の方法でインタリーブされてもよい。 - 構文解析が成功し、
early errors が見つからなかった場合、パースツリーのルートであるParse Node （goalSymbol のインスタンス）を返す。 - それ以外の場合、解析エラーおよび/または
early errors を表す 1 つ以上のSyntaxError オブジェクトのリスト を返す。複数の解析エラーまたはearly error がある場合、そのリスト内のエラーオブジェクトの数や順序は実装定義 だが、少なくとも 1 つは存在しなければならない。
あるテキストに特定の場所で
詳細は
11.2 ソースコードの種類
ECMAScript コードには4つの種類がある：
-
グローバルコードは、ECMAScript の
Script として扱われるソーステキストである。特定のScript のグローバルコードには、FunctionDeclaration 、FunctionExpression 、GeneratorDeclaration 、GeneratorExpression 、AsyncFunctionDeclaration 、AsyncFunctionExpression 、AsyncGeneratorDeclaration 、AsyncGeneratorExpression 、MethodDefinition 、ArrowFunction 、AsyncArrowFunction 、ClassDeclaration 、またはClassExpression の一部として構文解析されるソーステキストは含まれない。 -
eval コードは、組み込みの
eval関数に渡されたソーステキストである。より正確には、組み込みのeval関数のパラメータがString である 場合、それは ECMAScript のScript として扱われる。evalのある呼び出しの eval コードは、そのScript のグローバルコード部分である。 -
関数コードは、ECMAScript の
関数オブジェクト の [[ECMAScriptCode]] および [[FormalParameters]] 内部スロット（10.2 参照）に値を与えるために構文解析されるソーステキストである。特定の ECMAScript 関数の関数コードには、入れ子になったFunctionDeclaration 、FunctionExpression 、GeneratorDeclaration 、GeneratorExpression 、AsyncFunctionDeclaration 、AsyncFunctionExpression 、AsyncGeneratorDeclaration 、AsyncGeneratorExpression 、MethodDefinition 、ArrowFunction 、AsyncArrowFunction 、ClassDeclaration 、またはClassExpression の関数コードとして構文解析されるソーステキストは含まれない。さらに、上記のソーステキストが次のように構文解析される場合：
FormalParameters およびFunctionBody がFunctionDeclaration またはFunctionExpression の場合、FormalParameters およびGeneratorBody がGeneratorDeclaration またはGeneratorExpression の場合、FormalParameters およびAsyncFunctionBody がAsyncFunctionDeclaration またはAsyncFunctionExpression の場合、FormalParameters およびAsyncGeneratorBody がAsyncGeneratorDeclaration またはAsyncGeneratorExpression の場合、
その場合、宣言または式の
BindingIdentifier （存在する場合）によってマッチされるソーステキスト も、その関数の関数コードに含まれる。 -
モジュールコードは、
ModuleBody として提供されるコードである。これは、モジュールが初期化されるときに直接評価されるコードである。特定のモジュールのモジュールコードには、入れ子になったFunctionDeclaration 、FunctionExpression 、GeneratorDeclaration 、GeneratorExpression 、AsyncFunctionDeclaration 、AsyncFunctionExpression 、AsyncGeneratorDeclaration 、AsyncGeneratorExpression 、MethodDefinition 、ArrowFunction 、AsyncArrowFunction 、ClassDeclaration 、またはClassExpression の一部として構文解析されるソーステキストは含まれない。
関数コードは通常、関数定義（
関数コードに
11.2.1 ディレクティブプロローグと use strict ディレクティブ
ディレクティブプロローグとは、
use strict
ディレクティブとは、"use strict" または 'use strict' というコードポイント列であるものである。
11.2.2 厳格モードコード
ECMAScript の構文単位は、無制限モードまたは厳格モードの構文と意味（
-
グローバルコード が、ディレクティブプロローグ の先頭にuse strict ディレクティブ を含む場合。 -
モジュールコード は常に厳格モードコードである。 -
すべての
ClassDeclaration またはClassExpression の部分は厳格モードコードである。 -
eval コード が、ディレクティブプロローグ の先頭にuse strict ディレクティブ を含む場合、またはevalへの呼び出しがdirect eval であり、その呼び出し元が厳格モードコードである場合。 -
関数コード の関連するFunctionDeclaration 、FunctionExpression 、GeneratorDeclaration 、GeneratorExpression 、AsyncFunctionDeclaration 、AsyncFunctionExpression 、AsyncGeneratorDeclaration 、AsyncGeneratorExpression 、MethodDefinition 、ArrowFunction 、またはAsyncArrowFunction が厳格モードコード内に含まれている場合、または関数の [[ECMAScriptCode]] 内部スロットの値を生成するコードの先頭にディレクティブプロローグ があり、そこにuse strict ディレクティブ を含む場合。 -
組み込みの Function、Generator、AsyncFunction、AsyncGenerator
constructor に引数として渡される関数コード は、最後の引数がString であり 、それが処理されたときFunctionBody の先頭にディレクティブプロローグ があり、そこにuse strict ディレクティブ を含む場合は厳格モードコードである。
厳格モードコードでない ECMAScript コードは、非厳格コード と呼ばれる。
11.2.2.1 静的セマンティクス: IsStrict ( node )
抽象操作 IsStrict は、引数 node（
- もし
node にマッチしたソーステキスト が厳格モードコード であればtrue を返し、そうでなければfalse を返す。
11.2.3 非ECMAScript関数
ECMAScript の実装は、評価動作が
12 ECMAScript Language: Lexical Grammar
The source text of an ECMAScript
There are several situations where the identification of lexical input elements is sensitive to the
syntactic grammar context that is consuming the input elements. This requires multiple
The use of multiple lexical goals ensures that there are no lexical ambiguities that would affect
automatic semicolon insertion. For example, there are no syntactic grammar contexts where both a
leading division or division-assignment, and a leading
a = b
/hi/g.exec(c).map(d);where the first non-whitespace, non-comment code point after a
a = b / hi / g.exec(c).map(d);Syntax
12.1 Unicode Format-Control Characters
The Unicode format-control characters (i.e., the characters in category “Cf” in the Unicode Character Database such as LEFT-TO-RIGHT MARK or RIGHT-TO-LEFT MARK) are control codes used to control the formatting of a range of text in the absence of higher-level protocols for this (such as mark-up languages).
It is useful to allow format-control characters in source text to facilitate editing and display. All format control characters may be used within comments, and within string literals, template literals, and regular expression literals.
U+FEFF (ZERO WIDTH NO-BREAK SPACE) is a format-control character used primarily at the start of a
text to mark it as Unicode and to allow detection of the text's encoding and byte order.
<ZWNBSP> characters intended for this purpose can sometimes also appear after the start of a
text, for example as a result of concatenating files. In
12.2 White Space
White space code points are used to improve source text readability and to separate tokens
(indivisible lexical units) from each other, but are otherwise insignificant. White space code
points may occur between any two tokens and at the start or end of input. White space code points
may occur within a
The ECMAScript white space code points are listed in
| Code Points | Name | Abbreviation |
|---|---|---|
U+0009
|
CHARACTER TABULATION | <TAB> |
U+000B
|
LINE TABULATION | <VT> |
U+000C
|
FORM FEED (FF) | <FF> |
U+FEFF
|
ZERO WIDTH NO-BREAK SPACE | <ZWNBSP> |
| any code point in general category “Space_Separator” | <USP> |
U+0020 (SPACE) and U+00A0 (NO-BREAK SPACE) code points are part of <USP>.
Other than for the code points listed in
Syntax
12.3 Line Terminators
Like white space code points, line terminator code points are used to improve source text readability
and to separate tokens (indivisible lexical units) from each other. However, unlike white space code
points, line terminators have some influence over the behaviour of the syntactic grammar. In
general, line terminators may occur between any two tokens, but there are a few places where they
are forbidden by the syntactic grammar. Line terminators also affect the process of automatic
semicolon insertion (
A line terminator can occur within a
Line terminators are included in the set of white space code points that are matched by the
\s class in regular expressions.
The ECMAScript line terminator code points are listed in
| Code Point | Unicode Name | Abbreviation |
|---|---|---|
U+000A
|
LINE FEED (LF) | <LF> |
U+000D
|
CARRIAGE RETURN (CR) | <CR> |
U+2028
|
LINE SEPARATOR | <LS> |
U+2029
|
PARAGRAPH SEPARATOR | <PS> |
Only the Unicode code points in
Syntax
12.4 Comments
Comments can be either single or multi-line. Multi-line comments cannot nest.
Because a single-line comment can contain any Unicode code point except a // marker to the end of the line. However, the
Comments behave like white space and are discarded except that, if a
Syntax
A number of productions in this section are given alternative definitions in section
12.5 Hashbang Comments
Hashbang Comments are location-sensitive and like other types of comments are discarded from the stream of input elements for the syntactic grammar.
Syntax
12.6 Tokens
Syntax
The
12.7 Names and Keywords
This standard specifies specific code point additions: U+0024 (DOLLAR SIGN) and U+005F (LOW
LINE) are permitted anywhere in an
Syntax
The definitions of the nonterminal
The nonterminal _ via
The sets of code points with Unicode properties “ID_Start” and “ID_Continue” include, respectively, the code points with Unicode properties “Other_ID_Start” and “Other_ID_Continue”.
12.7.1 Identifier Names
Unicode escape sequences are permitted in an \ preceding the \
Two
12.7.1.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
IdentifierCodePoint ofUnicodeEscapeSequence is not some Unicode code point matched by theIdentifierStartChar lexical grammar production.
-
It is a Syntax Error if the
IdentifierCodePoint ofUnicodeEscapeSequence is not some Unicode code point matched by theIdentifierPartChar lexical grammar production.
12.7.1.2 Static Semantics: IdentifierCodePoints
The
- Let cp be the
IdentifierCodePoint ofIdentifierStart . - Return « cp ».
- Let cps be the
IdentifierCodePoints of the derivedIdentifierName . - Let cp be the
IdentifierCodePoint ofIdentifierPart . - Return the
list-concatenation of cps and « cp ».
12.7.1.3 Static Semantics: IdentifierCodePoint
The
- Return the code point matched by
IdentifierStartChar .
- Return the code point matched by
IdentifierPartChar .
- Return the code point whose numeric value is the MV of
Hex4Digits .
- Return the code point whose numeric value is the MV of
CodePoint .
12.7.2 Keywords and Reserved Words
A keyword is a token that matches fixed width font, in some
syntactic production. The keywords of ECMAScript include if, while,
async, await, and many others.
A reserved word is an if and while are reserved words.
await is reserved only inside async functions and modules. async is
not reserved; it can be used as a variable name or statement label without restriction.
This specification uses a combination of grammatical productions and await and yield, are unconditionally reserved. Exceptions
for await and yield are specified in
-
Those that are always allowed as identifiers, and are not keywords, such as
Math,window,toString, and_; -
Those that are never allowed as identifiers, namely the
ReservedWord s listed below exceptawaitandyield; -
Those that are contextually allowed as identifiers, namely
awaitandyield; -
Those that are contextually disallowed as identifiers, in
strict mode code :let,static,implements,interface,package,private,protected, andpublic; -
Those that are always allowed as identifiers, but also appear as keywords within certain syntactic productions, at places where
Identifier is not allowed:as,async,from,get,meta,of,set, andtarget.
The term conditional keyword, or contextual keyword, is sometimes used to refer to the keywords that fall in the last three categories, and thus can be used as identifiers in some contexts and as keywords in others.
Syntax
Per \
An \ els\u{65}. The
enum is not currently used as a keyword in this specification. It is a
future reserved word, set aside for use as a keyword in future language
extensions.
Similarly, implements, interface, package,
private, protected, and public are future
reserved words in
12.8 Punctuators
Syntax
12.9 Literals
12.9.1 Null Literals
Syntax
12.9.2 Boolean Literals
Syntax
12.9.3 Numeric Literals
Syntax
The
For example: 3in is an error and not the two input elements 3
and in.
12.9.3.1 Static Semantics: Early Errors
- It is a Syntax Error if
IsStrict (this production) istrue .
12.9.3.2 Static Semantics: MV
A numeric literal stands for a value of the
-
The MV of
DecimalLiteral :: DecimalIntegerLiteral . DecimalDigits DecimalIntegerLiteral plus (the MV ofDecimalDigits × 10-n), where n is the number of code points inDecimalDigits , excluding all occurrences ofNumericLiteralSeparator . -
The MV of
DecimalLiteral :: DecimalIntegerLiteral . ExponentPart DecimalIntegerLiteral × 10e, where e is the MV ofExponentPart . -
The MV of
DecimalLiteral :: DecimalIntegerLiteral . DecimalDigits ExponentPart DecimalIntegerLiteral plus (the MV ofDecimalDigits × 10-n)) × 10e, where n is the number of code points inDecimalDigits , excluding all occurrences ofNumericLiteralSeparator and e is the MV ofExponentPart . -
The MV of
DecimalLiteral :: . DecimalDigits DecimalDigits × 10-n, where n is the number of code points inDecimalDigits , excluding all occurrences ofNumericLiteralSeparator . -
The MV of
DecimalLiteral :: . DecimalDigits ExponentPart DecimalDigits × 10e - n, where n is the number of code points inDecimalDigits , excluding all occurrences ofNumericLiteralSeparator , and e is the MV ofExponentPart . -
The MV of
DecimalLiteral :: DecimalIntegerLiteral ExponentPart DecimalIntegerLiteral × 10e, where e is the MV ofExponentPart . -
The MV of
DecimalIntegerLiteral :: 0 -
The MV of
DecimalIntegerLiteral :: NonZeroDigit NumericLiteralSeparator opt DecimalDigits NonZeroDigit × 10n) plus the MV ofDecimalDigits , where n is the number of code points inDecimalDigits , excluding all occurrences ofNumericLiteralSeparator . -
The MV of
DecimalDigits :: DecimalDigits DecimalDigit DecimalDigits × 10) plus the MV ofDecimalDigit . -
The MV of
DecimalDigits :: DecimalDigits NumericLiteralSeparator DecimalDigit DecimalDigits × 10) plus the MV ofDecimalDigit . -
The MV of
ExponentPart :: ExponentIndicator SignedInteger SignedInteger . -
The MV of
SignedInteger :: - DecimalDigits DecimalDigits . -
The MV of
DecimalDigit :: 0 HexDigit :: 0 OctalDigit :: 0 LegacyOctalEscapeSequence :: 0 BinaryDigit :: 0 -
The MV of
DecimalDigit :: 1 NonZeroDigit :: 1 HexDigit :: 1 OctalDigit :: 1 BinaryDigit :: 1 -
The MV of
DecimalDigit :: 2 NonZeroDigit :: 2 HexDigit :: 2 OctalDigit :: 2 -
The MV of
DecimalDigit :: 3 NonZeroDigit :: 3 HexDigit :: 3 OctalDigit :: 3 -
The MV of
DecimalDigit :: 4 NonZeroDigit :: 4 HexDigit :: 4 OctalDigit :: 4 -
The MV of
DecimalDigit :: 5 NonZeroDigit :: 5 HexDigit :: 5 OctalDigit :: 5 -
The MV of
DecimalDigit :: 6 NonZeroDigit :: 6 HexDigit :: 6 OctalDigit :: 6 -
The MV of
DecimalDigit :: 7 NonZeroDigit :: 7 HexDigit :: 7 OctalDigit :: 7 -
The MV of
DecimalDigit :: 8 NonZeroDigit :: 8 NonOctalDigit :: 8 HexDigit :: 8 -
The MV of
DecimalDigit :: 9 NonZeroDigit :: 9 NonOctalDigit :: 9 HexDigit :: 9 -
The MV of
HexDigit :: a HexDigit :: A -
The MV of
HexDigit :: b HexDigit :: B -
The MV of
HexDigit :: c HexDigit :: C -
The MV of
HexDigit :: d HexDigit :: D -
The MV of
HexDigit :: e HexDigit :: E -
The MV of
HexDigit :: f HexDigit :: F -
The MV of
BinaryDigits :: BinaryDigits BinaryDigit BinaryDigits × 2) plus the MV ofBinaryDigit . -
The MV of
BinaryDigits :: BinaryDigits NumericLiteralSeparator BinaryDigit BinaryDigits × 2) plus the MV ofBinaryDigit . -
The MV of
OctalDigits :: OctalDigits OctalDigit OctalDigits × 8) plus the MV ofOctalDigit . -
The MV of
OctalDigits :: OctalDigits NumericLiteralSeparator OctalDigit OctalDigits × 8) plus the MV ofOctalDigit . -
The MV of
LegacyOctalIntegerLiteral :: LegacyOctalIntegerLiteral OctalDigit LegacyOctalIntegerLiteral times 8) plus the MV ofOctalDigit . -
The MV of
NonOctalDecimalIntegerLiteral :: LegacyOctalLikeDecimalIntegerLiteral NonOctalDigit LegacyOctalLikeDecimalIntegerLiteral times 10) plus the MV ofNonOctalDigit . -
The MV of
NonOctalDecimalIntegerLiteral :: NonOctalDecimalIntegerLiteral DecimalDigit NonOctalDecimalIntegerLiteral times 10) plus the MV ofDecimalDigit . -
The MV of
LegacyOctalLikeDecimalIntegerLiteral :: LegacyOctalLikeDecimalIntegerLiteral OctalDigit LegacyOctalLikeDecimalIntegerLiteral times 10) plus the MV ofOctalDigit . -
The MV of
HexDigits :: HexDigits HexDigit HexDigits × 16) plus the MV ofHexDigit . -
The MV of
HexDigits :: HexDigits NumericLiteralSeparator HexDigit HexDigits × 16) plus the MV ofHexDigit .
12.9.3.3 Static Semantics: NumericValue
The
- Return
RoundMVResult (MV ofDecimalLiteral ).
- Return
𝔽 (MV ofNonDecimalIntegerLiteral ).
- Return
𝔽 (MV ofLegacyOctalIntegerLiteral ).
- Return the
BigInt value for the MV ofNonDecimalIntegerLiteral .
- Return
0 ℤ.
- Return the
BigInt value for the MV ofNonZeroDigit .
- Let n be the number of code points in
DecimalDigits , excluding all occurrences ofNumericLiteralSeparator . - Let mv be (the MV of
NonZeroDigit × 10n) plus the MV ofDecimalDigits . - Return
ℤ (mv).
12.9.4 String Literals
A string literal is 0 or more Unicode code points enclosed in single or double quotes.
Unicode code points may also be represented by an escape sequence. All code points may
appear literally in a string literal except for the closing quote code points, U+005C
(REVERSE SOLIDUS), U+000D (CARRIAGE RETURN), and U+000A (LINE FEED). Any code points may
appear in the form of an escape sequence. String literals evaluate to ECMAScript String
values. When generating these String values Unicode code points are UTF-16 encoded as
defined in
Syntax
The definition of the nonterminal
<LF> and <CR> cannot appear in a string literal, except as part of a \n or
\u000A.
12.9.4.1 Static Semantics: Early Errors
- It is a Syntax Error if
IsStrict (this production) istrue .
It is possible for string literals to precede a
function invalid() { "\7"; "use strict"; }12.9.4.2 Static Semantics: SV
The
A string literal stands for a value of the
-
The SV of
StringLiteral :: " " -
The SV of
StringLiteral :: ' ' -
The SV of
DoubleStringCharacters :: DoubleStringCharacter DoubleStringCharacters string-concatenation of the SV ofDoubleStringCharacter and the SV ofDoubleStringCharacters . -
The SV of
SingleStringCharacters :: SingleStringCharacter SingleStringCharacters string-concatenation of the SV ofSingleStringCharacter and the SV ofSingleStringCharacters . -
The SV of
DoubleStringCharacter :: SourceCharacter but not one of " or\ orLineTerminator UTF16EncodeCodePoint on the code point matched bySourceCharacter . -
The SV of
DoubleStringCharacter :: <LS> -
The SV of
DoubleStringCharacter :: <PS> -
The SV of
DoubleStringCharacter :: LineContinuation -
The SV of
SingleStringCharacter :: SourceCharacter but not one of ' or\ orLineTerminator UTF16EncodeCodePoint on the code point matched bySourceCharacter . -
The SV of
SingleStringCharacter :: <LS> -
The SV of
SingleStringCharacter :: <PS> -
The SV of
SingleStringCharacter :: LineContinuation -
The SV of
EscapeSequence :: 0 -
The SV of
CharacterEscapeSequence :: SingleEscapeCharacter SingleEscapeCharacter according toTable 37 .
| Escape Sequence | Code Unit Value | Unicode Character Name | Symbol |
|---|---|---|---|
\b
|
0x0008
|
BACKSPACE | <BS> |
\t
|
0x0009
|
CHARACTER TABULATION | <HT> |
\n
|
0x000A
|
LINE FEED (LF) | <LF> |
\v
|
0x000B
|
LINE TABULATION | <VT> |
\f
|
0x000C
|
FORM FEED (FF) | <FF> |
\r
|
0x000D
|
CARRIAGE RETURN (CR) | <CR> |
\"
|
0x0022
|
QUOTATION MARK |
"
|
\'
|
0x0027
|
APOSTROPHE |
'
|
\\
|
0x005C
|
REVERSE SOLIDUS |
\
|
-
The SV of
NonEscapeCharacter :: SourceCharacter but not one of EscapeCharacter orLineTerminator UTF16EncodeCodePoint on the code point matched bySourceCharacter . -
The SV of
EscapeSequence :: LegacyOctalEscapeSequence LegacyOctalEscapeSequence . -
The SV of
NonOctalDecimalEscapeSequence :: 8 -
The SV of
NonOctalDecimalEscapeSequence :: 9 -
The SV of
HexEscapeSequence :: x HexDigit HexDigit HexEscapeSequence . -
The SV of
Hex4Digits :: HexDigit HexDigit HexDigit HexDigit Hex4Digits . -
The SV of
UnicodeEscapeSequence :: u{ CodePoint } UTF16EncodeCodePoint on the MV ofCodePoint . -
The SV of
TemplateEscapeSequence :: 0
12.9.4.3 Static Semantics: MV
-
The MV of
LegacyOctalEscapeSequence :: ZeroToThree OctalDigit ZeroToThree ) plus the MV ofOctalDigit . -
The MV of
LegacyOctalEscapeSequence :: FourToSeven OctalDigit FourToSeven ) plus the MV ofOctalDigit . -
The MV of
LegacyOctalEscapeSequence :: ZeroToThree OctalDigit OctalDigit ZeroToThree ) plus (8 times the MV of the firstOctalDigit ) plus the MV of the secondOctalDigit . -
The MV of
ZeroToThree :: 0 -
The MV of
ZeroToThree :: 1 -
The MV of
ZeroToThree :: 2 -
The MV of
ZeroToThree :: 3 -
The MV of
FourToSeven :: 4 -
The MV of
FourToSeven :: 5 -
The MV of
FourToSeven :: 6 -
The MV of
FourToSeven :: 7 -
The MV of
HexEscapeSequence :: x HexDigit HexDigit HexDigit ) plus the MV of the secondHexDigit . -
The MV of
Hex4Digits :: HexDigit HexDigit HexDigit HexDigit HexDigit ) plus (0x100 × the MV of the secondHexDigit ) plus (0x10 × the MV of the thirdHexDigit ) plus the MV of the fourthHexDigit .
12.9.5 Regular Expression Literals
A regular expression literal is an input element that is converted to a RegExp object
(see === to each other even if the two
literals' contents are identical. A RegExp object may also be created at runtime by
new RegExp or calling the RegExp
The productions below describe the syntax for a regular expression literal and are used by the
input element scanner to find the end of the regular expression literal. The source text
comprising the
An implementation may extend the ECMAScript Regular Expression grammar defined in
Syntax
Regular expression literals may not be empty; instead of representing an empty regular
expression literal, the code unit sequence // starts a single-line comment.
To specify an empty regular expression, use: /(?:)/.
12.9.5.1 Static Semantics: BodyText
The
- Return the source text that was recognized as
RegularExpressionBody .
12.9.5.2 Static Semantics: FlagText
The
- Return the source text that was recognized as
RegularExpressionFlags .
12.9.6 Template Literal Lexical Components
Syntax
12.9.6.1 Static Semantics: TV
The
-
The TV of
NoSubstitutionTemplate :: ` ` -
The TV of
TemplateHead :: ` ${ -
The TV of
TemplateMiddle :: } ${ -
The TV of
TemplateTail :: } ` -
The TV of
TemplateCharacters :: TemplateCharacter TemplateCharacters undefined if the TV ofTemplateCharacter isundefined or the TV ofTemplateCharacters isundefined . Otherwise, it is thestring-concatenation of the TV ofTemplateCharacter and the TV ofTemplateCharacters . -
The TV of
TemplateCharacter :: SourceCharacter but not one of ` or\ or$ orLineTerminator UTF16EncodeCodePoint on the code point matched bySourceCharacter . -
The TV of
TemplateCharacter :: $ -
The TV of
TemplateCharacter :: \ TemplateEscapeSequence SV ofTemplateEscapeSequence . -
The TV of
TemplateCharacter :: \ NotEscapeSequence undefined . -
The TV of
TemplateCharacter :: LineTerminatorSequence TRV ofLineTerminatorSequence . -
The TV of
LineContinuation :: \ LineTerminatorSequence
12.9.6.2 Static Semantics: TRV
The
-
The TRV of
NoSubstitutionTemplate :: ` ` -
The TRV of
TemplateHead :: ` ${ -
The TRV of
TemplateMiddle :: } ${ -
The TRV of
TemplateTail :: } ` -
The TRV of
TemplateCharacters :: TemplateCharacter TemplateCharacters string-concatenation of the TRV ofTemplateCharacter and the TRV ofTemplateCharacters . -
The TRV of
TemplateCharacter :: SourceCharacter but not one of ` or\ or$ orLineTerminator UTF16EncodeCodePoint on the code point matched bySourceCharacter . -
The TRV of
TemplateCharacter :: $ -
The TRV of
TemplateCharacter :: \ TemplateEscapeSequence string-concatenation of the code unit 0x005C (REVERSE SOLIDUS) and the TRV ofTemplateEscapeSequence . -
The TRV of
TemplateCharacter :: \ NotEscapeSequence string-concatenation of the code unit 0x005C (REVERSE SOLIDUS) and the TRV ofNotEscapeSequence . -
The TRV of
TemplateEscapeSequence :: 0 -
The TRV of
NotEscapeSequence :: 0 DecimalDigit string-concatenation of the code unit 0x0030 (DIGIT ZERO) and the TRV ofDecimalDigit . -
The TRV of
NotEscapeSequence :: x [lookahead ∉ HexDigit ] -
The TRV of
NotEscapeSequence :: x HexDigit [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0078 (LATIN SMALL LETTER X) and the TRV ofHexDigit . -
The TRV of
NotEscapeSequence :: u [lookahead ∉ HexDigit ][lookahead ≠ { ] -
The TRV of
NotEscapeSequence :: u HexDigit [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U) and the TRV ofHexDigit . -
The TRV of
NotEscapeSequence :: u HexDigit HexDigit [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U), the TRV of the firstHexDigit , and the TRV of the secondHexDigit . -
The TRV of
NotEscapeSequence :: u HexDigit HexDigit HexDigit [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U), the TRV of the firstHexDigit , the TRV of the secondHexDigit , and the TRV of the thirdHexDigit . -
The TRV of
NotEscapeSequence :: u { [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U) and the code unit 0x007B (LEFT CURLY BRACKET). -
The TRV of
NotEscapeSequence :: u { NotCodePoint [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U), the code unit 0x007B (LEFT CURLY BRACKET), and the TRV ofNotCodePoint . -
The TRV of
NotEscapeSequence :: u { CodePoint [lookahead ∉ HexDigit ][lookahead ≠ } ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U), the code unit 0x007B (LEFT CURLY BRACKET), and the TRV ofCodePoint . -
The TRV of
DecimalDigit :: one of 0 1 2 3 4 5 6 7 8 9 UTF16EncodeCodePoint on the single code point matched by this production. -
The TRV of
CharacterEscapeSequence :: NonEscapeCharacter SV ofNonEscapeCharacter . -
The TRV of
SingleEscapeCharacter :: one of ' " \ b f n r t v UTF16EncodeCodePoint on the single code point matched by this production. -
The TRV of
HexEscapeSequence :: x HexDigit HexDigit string-concatenation of the code unit 0x0078 (LATIN SMALL LETTER X), the TRV of the firstHexDigit , and the TRV of the secondHexDigit . -
The TRV of
UnicodeEscapeSequence :: u Hex4Digits string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U) and the TRV ofHex4Digits . -
The TRV of
UnicodeEscapeSequence :: u{ CodePoint } string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U), the code unit 0x007B (LEFT CURLY BRACKET), the TRV ofCodePoint , and the code unit 0x007D (RIGHT CURLY BRACKET). -
The TRV of
Hex4Digits :: HexDigit HexDigit HexDigit HexDigit string-concatenation of the TRV of the firstHexDigit , the TRV of the secondHexDigit , the TRV of the thirdHexDigit , and the TRV of the fourthHexDigit . -
The TRV of
HexDigits :: HexDigits HexDigit string-concatenation of the TRV ofHexDigits and the TRV ofHexDigit . -
The TRV of
HexDigit :: one of 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F UTF16EncodeCodePoint on the single code point matched by this production. -
The TRV of
LineContinuation :: \ LineTerminatorSequence string-concatenation of the code unit 0x005C (REVERSE SOLIDUS) and the TRV ofLineTerminatorSequence . -
The TRV of
LineTerminatorSequence :: <LF> -
The TRV of
LineTerminatorSequence :: <CR> -
The TRV of
LineTerminatorSequence :: <LS> -
The TRV of
LineTerminatorSequence :: <PS> -
The TRV of
LineTerminatorSequence :: <CR> <LF>
12.10 Automatic Semicolon Insertion
Most ECMAScript statements and declarations must be terminated with a semicolon. Such semicolons may always appear explicitly in the source text. For convenience, however, such semicolons may be omitted from the source text in certain situations. These situations are described by saying that semicolons are automatically inserted into the source code token stream in those situations.
12.10.1 Rules of Automatic Semicolon Insertion
In the following rules, “token” means the actual recognized lexical token determined using the
current lexical
There are three basic rules of semicolon insertion:
-
When, as the source text is parsed from left to right, a token (called the offending token) is encountered that is not allowed by any production of the grammar, then a semicolon is automatically inserted before the offending token if one or more of the following conditions is true:
-
The offending token is separated from the previous token by at least one
LineTerminator . -
The offending token is
}. -
The previous token is
)and the inserted semicolon would then be parsed as the terminating semicolon of a do-while statement (14.7.2 ).
-
The offending token is separated from the previous token by at least one
- When, as the source text is parsed from left to right, the end of the input stream of tokens is encountered and the parser is unable to parse the input token stream as a single instance of the goal nonterminal, then a semicolon is automatically inserted at the end of the input stream.
-
When, as the source text is parsed from left to right, a token is encountered that is
allowed by some production of the grammar, but the production is a restricted
production and the token would be the first token for a terminal or nonterminal
immediately following the annotation “[no
LineTerminator here]” within the restricted production (and therefore such a token is called a restricted token), and the restricted token is separated from the previous token by at least oneLineTerminator , then a semicolon is automatically inserted before the restricted token.
However, there is an additional overriding condition on the preceding rules: a semicolon is never
inserted automatically if the semicolon would then be parsed as an empty statement or if that
semicolon would become one of the two semicolons in the header of a for statement
(see
The following are the only restricted productions in the grammar:
The practical effect of these restricted productions is as follows:
-
When a
++or--token is encountered where the parser would treat it as a postfix operator, and at least oneLineTerminator occurred between the preceding token and the++or--token, then a semicolon is automatically inserted before the++or--token. -
When a
continue,break,return,throw, oryieldtoken is encountered and aLineTerminator is encountered before the next token, a semicolon is automatically inserted after thecontinue,break,return,throw, oryieldtoken. -
When arrow function parameter(s) are followed by a
LineTerminator before a=>token, a semicolon is automatically inserted and the punctuator causes a syntax error. -
When an
asynctoken is followed by aLineTerminator before afunctionorIdentifierName or(token, a semicolon is automatically inserted and theasynctoken is not treated as part of the same expression or class element as the following tokens. -
When an
asynctoken is followed by aLineTerminator before a*token, a semicolon is automatically inserted and the punctuator causes a syntax error.
The resulting practical advice to ECMAScript programmers is:
-
A postfix
++or--operator should be on the same line as its operand. -
An
Expression in areturnorthrowstatement or anAssignmentExpression in ayieldexpression should start on the same line as thereturn,throw, oryieldtoken. -
A
LabelIdentifier in abreakorcontinuestatement should be on the same line as thebreakorcontinuetoken. -
The end of an arrow function's parameter(s) and its
=>should be on the same line. -
The
asynctoken preceding an asynchronous function or method should be on the same line as the immediately following token.
12.10.2 Examples of Automatic Semicolon Insertion
This section is non-normative.The source
{ 1 2 } 3is not a valid sentence in the ECMAScript grammar, even with the automatic semicolon insertion rules. In contrast, the source
{ 1
2 } 3is also not a valid ECMAScript sentence, but is transformed by automatic semicolon insertion into the following:
{ 1
;2 ;} 3;which is a valid ECMAScript sentence.
The source
for (a; b
)is not a valid ECMAScript sentence and is not altered by automatic semicolon insertion because
the semicolon is needed for the header of a for statement. Automatic semicolon
insertion never inserts one of the two semicolons in the header of a for statement.
The source
return
a + bis transformed by automatic semicolon insertion into the following:
return;
a + b;The expression a + b is not treated as a value to be returned by the
return statement, because a return.
The source
a = b
++cis transformed by automatic semicolon insertion into the following:
a = b;
++c;The token ++ is not treated as a postfix operator applying to the variable
b, because a b and ++.
The source
if (a > b)
else c = dis not a valid ECMAScript sentence and is not altered by automatic semicolon insertion before the
else token, even though no production of the grammar applies at that point, because
an automatically inserted semicolon would then be parsed as an empty statement.
The source
a = b + c
(d + e).print()is not transformed by automatic semicolon insertion, because the parenthesized expression that begins the second line can be interpreted as an argument list for a function call:
a = b + c(d + e).print()In the circumstance that an assignment statement must begin with a left parenthesis, it is a good idea for the programmer to provide an explicit semicolon at the end of the preceding statement rather than to rely on automatic semicolon insertion.
12.10.3 Interesting Cases of Automatic Semicolon Insertion
This section is non-normative.ECMAScript programs can be written in a style with very few semicolons by relying on automatic semicolon insertion. As described above, semicolons are not inserted at every newline, and automatic semicolon insertion can depend on multiple tokens across line terminators.
As new syntactic features are added to ECMAScript, additional grammar productions could be added that cause lines relying on automatic semicolon insertion preceding them to change grammar productions when parsed.
For the purposes of this section, a case of automatic semicolon insertion is considered interesting if it is a place where a semicolon may or may not be inserted, depending on the source text which precedes it. The rest of this section describes a number of interesting cases of automatic semicolon insertion in this version of ECMAScript.
12.10.3.1 Interesting Cases of Automatic Semicolon Insertion in Statement Lists
In a
- An opening parenthesis (
(). Without a semicolon, the two lines together are treated as aCallExpression . - An opening square bracket (
[). Without a semicolon, the two lines together are treated as property access, rather than anArrayLiteral orArrayAssignmentPattern . - A template literal (
`). Without a semicolon, the two lines together are interpreted as a tagged Template (13.3.11 ), with the previous expression as theMemberExpression . - Unary
+or-. Without a semicolon, the two lines together are interpreted as a usage of the corresponding binary operator. - A RegExp literal. Without a semicolon, the two lines together may be
parsed instead as the
/MultiplicativeOperator , for example if the RegExp has flags.
12.10.3.2 Cases of Automatic Semicolon Insertion and “[no
LineTerminator here]”
This section is non-normative.
ECMAScript contains grammar productions which include “[no
The rest of this section describes a number of productions using “[no
12.10.3.2.1 List of Grammar Productions with Optional
Operands and “[no LineTerminator here]”
UpdateExpression .ContinueStatement .BreakStatement .ReturnStatement .YieldExpression .- Async Function Definitions (
15.8 ) with relation to Function Definitions (15.2 )
13 ECMAScript Language: Expressions
13.1 Identifiers
Syntax
yield and await are permitted as
let
await 0;13.1.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsStrict (this production) istrue and theStringValue ofIdentifier is either"arguments" or"eval" .
-
It is a Syntax Error if
IsStrict (this production) istrue .
-
It is a Syntax Error if the
goal symbol of the syntactic grammar isModule .
- It is a Syntax Error if this production has a [Yield] parameter.
- It is a Syntax Error if this production has an [Await] parameter.
-
It is a Syntax Error if this production has a [Yield] parameter and the
StringValue ofIdentifier is"yield" . -
It is a Syntax Error if this production has an [Await] parameter and the
StringValue ofIdentifier is"await" .
-
It is a Syntax Error if
IsStrict (this phrase) istrue and theStringValue ofIdentifierName is one of"implements" ,"interface" ,"let" ,"package" ,"private" ,"protected" ,"public" ,"static" , or"yield" . -
It is a Syntax Error if the
goal symbol of the syntactic grammar isModule and theStringValue ofIdentifierName is"await" . -
It is a Syntax Error if the
StringValue ofIdentifierName is theStringValue of anyReservedWord except foryieldorawait.
The
13.1.2 Static Semantics: StringValue
The
- Let idTextUnescaped be the
IdentifierCodePoints ofIdentifierName . - Return
CodePointsToString (idTextUnescaped).
- Return
"yield" .
- Return
"await" .
- Return the
StringValue ofIdentifierName .
- Return the
string-concatenation of 0x0023 (NUMBER SIGN) and theStringValue ofIdentifierName .
- Return the
SV ofStringLiteral .
13.1.3 Runtime Semantics: Evaluation
- Return ?
ResolveBinding (StringValue ofIdentifier ).
- Return ?
ResolveBinding ("yield" ).
- Return ?
ResolveBinding ("await" ).
The result of evaluating an
In yield may be used as an identifier. Evaluating the yield as if it was an
13.2 Primary Expression
Syntax
Supplemental Syntax
When processing an instance of the production
the interpretation of
13.2.1 The this Keyword
13.2.1.1 Runtime Semantics: Evaluation
- Return ?
ResolveThisBinding ().
13.2.2 Identifier Reference
See
13.2.3 Literals
Syntax
13.2.3.1 Runtime Semantics: Evaluation
- Return
null .
- If
BooleanLiteral is the tokenfalse, returnfalse . - If
BooleanLiteral is the tokentrue, returntrue .
- Return the
NumericValue ofNumericLiteral as defined in12.9.3 .
- Return the
SV ofStringLiteral as defined in12.9.4.2 .
13.2.4 Array Initializer
An
Array elements may be elided at the beginning, middle or end of the element list. Whenever a
comma in the element list is not preceded by an
Syntax
13.2.4.1 Runtime Semantics: ArrayAccumulation
The
- Return ?
ArrayAccumulation ofElision with arguments array and (nextIndex + 1).
- If
Elision is present, then- Set nextIndex to ?
ArrayAccumulation ofElision with arguments array and nextIndex.
- Set nextIndex to ?
- Let initResult be ?
Evaluation ofAssignmentExpression . - Let initValue be ?
GetValue (initResult). - Perform !
CreateDataPropertyOrThrow (array, !ToString (𝔽 (nextIndex)), initValue). - Return nextIndex + 1.
- If
Elision is present, then- Set nextIndex to ?
ArrayAccumulation ofElision with arguments array and nextIndex.
- Set nextIndex to ?
- Return ?
ArrayAccumulation ofSpreadElement with arguments array and nextIndex.
- Set nextIndex to ?
ArrayAccumulation ofElementList with arguments array and nextIndex. - If
Elision is present, then- Set nextIndex to ?
ArrayAccumulation ofElision with arguments array and nextIndex.
- Set nextIndex to ?
- Let initResult be ?
Evaluation ofAssignmentExpression . - Let initValue be ?
GetValue (initResult). - Perform !
CreateDataPropertyOrThrow (array, !ToString (𝔽 (nextIndex)), initValue). - Return nextIndex + 1.
- Set nextIndex to ?
ArrayAccumulation ofElementList with arguments array and nextIndex. - If
Elision is present, then- Set nextIndex to ?
ArrayAccumulation ofElision with arguments array and nextIndex.
- Set nextIndex to ?
- Return ?
ArrayAccumulation ofSpreadElement with arguments array and nextIndex.
- Let spreadRef be ?
Evaluation ofAssignmentExpression . - Let spreadObj be ?
GetValue (spreadRef). - Let iteratorRecord be ?
GetIterator (spreadObj,sync ). - Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , return nextIndex. - Perform !
CreateDataPropertyOrThrow (array, !ToString (𝔽 (nextIndex)), next). - Set nextIndex to nextIndex + 1.
- Let next be ?
13.2.4.2 Runtime Semantics: Evaluation
- Let array be !
ArrayCreate (0). - If
Elision is present, then- Perform ?
ArrayAccumulation ofElision with arguments array and 0.
- Perform ?
- Return array.
- Let array be !
ArrayCreate (0). - Perform ?
ArrayAccumulation ofElementList with arguments array and 0. - Return array.
- Let array be !
ArrayCreate (0). - Let nextIndex be ?
ArrayAccumulation ofElementList with arguments array and 0. - If
Elision is present, then- Perform ?
ArrayAccumulation ofElision with arguments array and nextIndex.
- Perform ?
- Return array.
13.2.5 Object Initializer
An object initializer is an expression describing the initialization of an Object,
written in a form resembling a literal. It is a list of zero or more pairs of
Syntax
In certain contexts,
13.2.5.1 Static Semantics: Early Errors
-
It is a Syntax Error if
HasDirectSuper ofMethodDefinition istrue . -
It is a Syntax Error if the
PrivateBoundIdentifiers ofMethodDefinition is not empty.
In addition to describing an actual object initializer the
- It is a Syntax Error if any source text is matched by this production.
This production exists so that
-
It is a Syntax Error if the
PropertyNameList ofPropertyDefinitionList contains any duplicate entries for"__proto__" and at least two of those entries were obtained from productions of the formPropertyDefinition : PropertyName : AssignmentExpression ObjectLiteral is contained within aScript that is being parsed forParseJSON (see step3 ofParseJSON ).
The
13.2.5.2 Static Semantics: IsComputedPropertyKey
The
- Return
false .
- Return
true .
13.2.5.3 Static Semantics: PropertyNameList
The
- Let propName be the
PropName ofPropertyDefinition . - If propName is
empty , return a new emptyList . - Return « propName ».
- Let list be the
PropertyNameList ofPropertyDefinitionList . - Let propName be the
PropName ofPropertyDefinition . - If propName is
empty , return list. - Return the
list-concatenation of list and « propName ».
13.2.5.4 Runtime Semantics: Evaluation
- Return
OrdinaryObjectCreate (%Object.prototype% ).
- Let obj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform ?
PropertyDefinitionEvaluation ofPropertyDefinitionList with argument obj. - Return obj.
- Return the
StringValue ofIdentifierName .
- Return the
SV ofStringLiteral .
- Let nbr be the
NumericValue ofNumericLiteral . - Return !
ToString (nbr).
- Let exprValue be ?
Evaluation ofAssignmentExpression . - Let propName be ?
GetValue (exprValue). - Return ?
ToPropertyKey (propName).
13.2.5.5 Runtime Semantics: PropertyDefinitionEvaluation
The
- Perform ?
PropertyDefinitionEvaluation ofPropertyDefinitionList with argument object. - Perform ?
PropertyDefinitionEvaluation ofPropertyDefinition with argument object. - Return
unused .
- Let exprValue be ?
Evaluation ofAssignmentExpression . - Let fromValue be ?
GetValue (exprValue). - Let excludedNames be a new empty
List . - Perform ?
CopyDataProperties (object, fromValue, excludedNames). - Return
unused .
- Let propName be the
StringValue ofIdentifierReference . - Let exprValue be ?
Evaluation ofIdentifierReference . - Let propValue be ?
GetValue (exprValue). Assert : object is an ordinary, extensible object with no non-configurable properties.- Perform !
CreateDataPropertyOrThrow (object, propName, propValue). - Return
unused .
- Let propKey be ?
Evaluation ofPropertyName . - If this
PropertyDefinition is contained within aScript that is being evaluated forParseJSON (see step6 ofParseJSON ), then- Let isProtoSetter be
false .
- Let isProtoSetter be
- Else if propKey is
"__proto__" andIsComputedPropertyKey ofPropertyName isfalse , then- Let isProtoSetter be
true .
- Let isProtoSetter be
- Else,
- Let isProtoSetter be
false .
- Let isProtoSetter be
- If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue and isProtoSetter isfalse , then- Let propValue be ?
NamedEvaluation ofAssignmentExpression with argument propKey.
- Let propValue be ?
- Else,
- Let exprValueRef be ?
Evaluation ofAssignmentExpression . - Let propValue be ?
GetValue (exprValueRef).
- Let exprValueRef be ?
- If isProtoSetter is
true , then- If propValue
is an Object or propValue isnull , then- Perform ! object.[[SetPrototypeOf]](propValue).
- Return
unused .
- If propValue
Assert : object is an ordinary, extensible object with no non-configurable properties.- Perform !
CreateDataPropertyOrThrow (object, propKey, propValue). - Return
unused .
- Perform ?
MethodDefinitionEvaluation ofMethodDefinition with arguments object andtrue . - Return
unused .
13.2.6 Function Defining Expressions
See
See
See
See
See
13.2.7 Regular Expression Literals
Syntax
See
13.2.7.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsValidRegularExpressionLiteral (RegularExpressionLiteral ) isfalse .
13.2.7.2 Static Semantics: IsValidRegularExpressionLiteral ( literal )
The abstract operation IsValidRegularExpressionLiteral takes argument literal (a
- Let flags be the
FlagText of literal. - If flags contains any code points other than
d,g,i,m,s,u,v, ory, or if flags contains any code point more than once, returnfalse . - If flags contains
u, let u betrue ; else let u befalse . - If flags contains
v, let v betrue ; else let v befalse . - Let patternText be the
BodyText of literal. - If u is
false and v isfalse , then- Let stringValue be
CodePointsToString (patternText). - Set patternText to the sequence of code points resulting from interpreting each of the 16-bit elements of stringValue as a Unicode BMP code point. UTF-16 decoding is not applied to the elements.
- Let stringValue be
- Let parseResult be
ParsePattern (patternText, u, v). - If parseResult is a
Parse Node , returntrue ; else returnfalse .
13.2.7.3 Runtime Semantics: Evaluation
- Let pattern be
CodePointsToString (BodyText ofRegularExpressionLiteral ). - Let flags be
CodePointsToString (FlagText ofRegularExpressionLiteral ). - Return !
RegExpCreate (pattern, flags).
13.2.8 Template Literals
Syntax
13.2.8.1 Static Semantics: Early Errors
-
It is a Syntax Error if the [Tagged] parameter was not set and
NoSubstitutionTemplate Contains NotEscapeSequence .
-
It is a Syntax Error if the number of elements in the
TemplateStrings ofTemplateLiteral with argumentfalse is greater than or equal to 232.
-
It is a Syntax Error if the [Tagged] parameter was not set and
TemplateHead Contains NotEscapeSequence .
-
It is a Syntax Error if the [Tagged] parameter was not set and
TemplateTail Contains NotEscapeSequence .
-
It is a Syntax Error if the [Tagged] parameter was not set and
TemplateMiddle Contains NotEscapeSequence .
13.2.8.2 Static Semantics: TemplateStrings
The
- Return «
TemplateString (NoSubstitutionTemplate , raw) ».
- Let head be «
TemplateString (TemplateHead , raw) ». - Let tail be the
TemplateStrings ofTemplateSpans with argument raw. - Return the
list-concatenation of head and tail.
- Return «
TemplateString (TemplateTail , raw) ».
- Let middle be the
TemplateStrings ofTemplateMiddleList with argument raw. - Let tail be «
TemplateString (TemplateTail , raw) ». - Return the
list-concatenation of middle and tail.
- Return «
TemplateString (TemplateMiddle , raw) ».
- Let front be the
TemplateStrings ofTemplateMiddleList with argument raw. - Let last be «
TemplateString (TemplateMiddle , raw) ». - Return the
list-concatenation of front and last.
13.2.8.3 Static Semantics: TemplateString ( templateToken, raw )
The abstract operation TemplateString takes arguments templateToken (a
This operation returns
13.2.8.4 GetTemplateObject ( templateLiteral )
The abstract operation GetTemplateObject takes argument templateLiteral (a
- Let realm be
the current Realm Record . - Let templateRegistry be realm.[[TemplateMap]].
- For each element e of templateRegistry, do
- If e.[[Site]] is
the same Parse Node as templateLiteral, then- Return e.[[Array]].
- If e.[[Site]] is
- Let rawStrings be the
TemplateStrings of templateLiteral with argumenttrue . Assert : rawStrings is aList of Strings.- Let cookedStrings be the
TemplateStrings of templateLiteral with argumentfalse . - Let count be the number of elements in the
List cookedStrings. Assert : count ≤ 232 - 1.- Let template be !
ArrayCreate (count). - Let rawObj be !
ArrayCreate (count). - Let index be 0.
- Repeat, while index < count,
- Let prop be !
ToString (𝔽 (index)). - Let cookedValue be cookedStrings[index].
- Perform !
DefinePropertyOrThrow (template, prop, PropertyDescriptor { [[Value]]: cookedValue, [[Writable]]:false , [[Enumerable]]:true , [[Configurable]]:false }). - Let rawValue be the String value rawStrings[index].
- Perform !
DefinePropertyOrThrow (rawObj, prop, PropertyDescriptor { [[Value]]: rawValue, [[Writable]]:false , [[Enumerable]]:true , [[Configurable]]:false }). - Set index to index + 1.
- Let prop be !
- Perform !
SetIntegrityLevel (rawObj,frozen ). - Perform !
DefinePropertyOrThrow (template,"raw" , PropertyDescriptor { [[Value]]: rawObj, [[Writable]]:false , [[Enumerable]]:false , [[Configurable]]:false }). - Perform !
SetIntegrityLevel (template,frozen ). - Append the
Record { [[Site]]: templateLiteral, [[Array]]: template } to realm.[[TemplateMap]]. - Return template.
The creation of a template object cannot result in an
Each
Future editions of this specification may define additional non-enumerable properties of template objects.
13.2.8.5 Runtime Semantics: SubstitutionEvaluation
The
- Return a new empty
List .
- Return ?
SubstitutionEvaluation ofTemplateMiddleList .
- Let subRef be ?
Evaluation ofExpression . - Let sub be ?
GetValue (subRef). - Return « sub ».
- Let preceding be ?
SubstitutionEvaluation ofTemplateMiddleList . - Let nextRef be ?
Evaluation ofExpression . - Let next be ?
GetValue (nextRef). - Return the
list-concatenation of preceding and « next ».
13.2.8.6 Runtime Semantics: Evaluation
- Return the
TV ofNoSubstitutionTemplate as defined in12.9.6 .
- Let head be the
TV ofTemplateHead as defined in12.9.6 . - Let subRef be ?
Evaluation ofExpression . - Let sub be ?
GetValue (subRef). - Let middle be ?
ToString (sub). - Let tail be ?
Evaluation ofTemplateSpans . - Return the
string-concatenation of head, middle, and tail.
The string conversion semantics applied to the String.prototype.concat rather than the + operator.
- Return the
TV ofTemplateTail as defined in12.9.6 .
- Let head be ?
Evaluation ofTemplateMiddleList . - Let tail be the
TV ofTemplateTail as defined in12.9.6 . - Return the
string-concatenation of head and tail.
- Let head be the
TV ofTemplateMiddle as defined in12.9.6 . - Let subRef be ?
Evaluation ofExpression . - Let sub be ?
GetValue (subRef). - Let middle be ?
ToString (sub). - Return the
string-concatenation of head and middle.
The string conversion semantics applied to the String.prototype.concat rather than the + operator.
- Let rest be ?
Evaluation ofTemplateMiddleList . - Let middle be the
TV ofTemplateMiddle as defined in12.9.6 . - Let subRef be ?
Evaluation ofExpression . - Let sub be ?
GetValue (subRef). - Let last be ?
ToString (sub). - Return the
string-concatenation of rest, middle, and last.
The string conversion semantics applied to the String.prototype.concat rather than the + operator.
13.2.9 The Grouping Operator
13.2.9.1 Static Semantics: Early Errors
13.2.9.2 Runtime Semantics: Evaluation
- Let expr be the
ParenthesizedExpression that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return ?
Evaluation of expr.
- Return ?
Evaluation ofExpression . This may be of type Reference.
This algorithm does not apply delete and
typeof may be applied to parenthesized expressions.
13.3 Left-Hand-Side Expressions
Syntax
Supplemental Syntax
When processing an instance of the production
the interpretation of
13.3.1 Static Semantics
13.3.1.1 Static Semantics: Early Errors
- It is a Syntax Error if any source text is matched by this production.
This production exists in order to prevent automatic semicolon insertion rules
(
a?.b
`c`so that it would be interpreted as two valid statements. The purpose is to maintain consistency with similar code without optional chaining:
a.b
`c`which is a valid statement and where automatic semicolon insertion does not apply.
-
It is a Syntax Error if the syntactic
goal symbol is notModule .
13.3.2 Property Accessors
Properties are accessed by name, using either the dot notation:
or the bracket notation:
The dot notation is explained by the following syntactic conversion:
is identical in its behaviour to
and similarly
is identical in its behaviour to
where <identifier-name-string> is the
13.3.2.1 Runtime Semantics: Evaluation
- Let baseReference be ?
Evaluation ofMemberExpression . - Let baseValue be ?
GetValue (baseReference). - Let strict be
IsStrict (thisMemberExpression ). - Return ?
EvaluatePropertyAccessWithExpressionKey (baseValue,Expression , strict).
- Let baseReference be ?
Evaluation ofMemberExpression . - Let baseValue be ?
GetValue (baseReference). - Let strict be
IsStrict (thisMemberExpression ). - Return
EvaluatePropertyAccessWithIdentifierKey (baseValue,IdentifierName , strict).
- Let baseReference be ?
Evaluation ofMemberExpression . - Let baseValue be ?
GetValue (baseReference). - Let fieldNameString be the
StringValue ofPrivateIdentifier . - Return
MakePrivateReference (baseValue, fieldNameString).
- Let baseReference be ?
Evaluation ofCallExpression . - Let baseValue be ?
GetValue (baseReference). - Let strict be
IsStrict (thisCallExpression ). - Return ?
EvaluatePropertyAccessWithExpressionKey (baseValue,Expression , strict).
- Let baseReference be ?
Evaluation ofCallExpression . - Let baseValue be ?
GetValue (baseReference). - Let strict be
IsStrict (thisCallExpression ). - Return
EvaluatePropertyAccessWithIdentifierKey (baseValue,IdentifierName , strict).
- Let baseReference be ?
Evaluation ofCallExpression . - Let baseValue be ?
GetValue (baseReference). - Let fieldNameString be the
StringValue ofPrivateIdentifier . - Return
MakePrivateReference (baseValue, fieldNameString).
13.3.3 EvaluatePropertyAccessWithExpressionKey ( baseValue, expression, strict )
The abstract operation EvaluatePropertyAccessWithExpressionKey takes arguments
baseValue (an
- Let propertyNameReference be ?
Evaluation of expression. - Let propertyNameValue be ?
GetValue (propertyNameReference). - NOTE: In most cases,
ToPropertyKey will be performed on propertyNameValue immediately after this step. However, in the case ofa[b] = c, it will not be performed until after evaluation ofc. - Return the
Reference Record { [[Base]]: baseValue, [[ReferencedName]]: propertyNameValue, [[Strict]]: strict, [[ThisValue]]:empty }.
13.3.4 EvaluatePropertyAccessWithIdentifierKey ( baseValue, identifierName, strict )
The abstract operation EvaluatePropertyAccessWithIdentifierKey takes arguments
baseValue (an
- Let propertyNameString be the
StringValue of identifierName. - Return the
Reference Record { [[Base]]: baseValue, [[ReferencedName]]: propertyNameString, [[Strict]]: strict, [[ThisValue]]:empty }.
13.3.5 The new Operator
13.3.5.1 Runtime Semantics: Evaluation
- Return ?
EvaluateNew (NewExpression ,empty ).
- Return ?
EvaluateNew (MemberExpression ,Arguments ).
13.3.5.1.1 EvaluateNew ( constructExpr, arguments )
The abstract operation EvaluateNew takes arguments constructExpr (a
- Let ref be ?
Evaluation of constructExpr. - Let constructor be ?
GetValue (ref). - If arguments is
empty , then- Let argList be a new empty
List .
- Let argList be a new empty
- Else,
- Let argList be ?
ArgumentListEvaluation of arguments.
- Let argList be ?
- If
IsConstructor (constructor) isfalse , throw aTypeError exception. - Return ?
Construct (constructor, argList).
13.3.6 Function Calls
13.3.6.1 Runtime Semantics: Evaluation
- Let expr be the
CallMemberExpression that iscovered byCoverCallExpressionAndAsyncArrowHead . - Let memberExpr be the
MemberExpression of expr. - Let arguments be the
Arguments of expr. - Let ref be ?
Evaluation of memberExpr. - Let func be ?
GetValue (ref). - If ref is a
Reference Record ,IsPropertyReference (ref) isfalse , and ref.[[ReferencedName]] is"eval" , then- If
SameValue (func,%eval% ) istrue , then- Let argList be ?
ArgumentListEvaluation of arguments. - If argList has no elements, return
undefined . - Let evalArg be the first element of argList.
- If
IsStrict (thisCallExpression ) istrue , let strictCaller betrue ; otherwise let strictCaller befalse . - Return
?
PerformEval (evalArg, strictCaller,true ).
- Let argList be ?
- If
- Let thisCall be this
CallExpression . - Let tailCall be
IsInTailPosition (thisCall). - Return ?
EvaluateCall (func, ref, arguments, tailCall).
A
- Let ref be ?
Evaluation ofCallExpression . - Let func be ?
GetValue (ref). - Let thisCall be this
CallExpression . - Let tailCall be
IsInTailPosition (thisCall). - Return ?
EvaluateCall (func, ref,Arguments , tailCall).
13.3.6.2 EvaluateCall ( func, ref, arguments, tailPosition )
The abstract operation EvaluateCall takes arguments func (an
- If ref is a
Reference Record , then- If
IsPropertyReference (ref) istrue , then- Let thisValue be
GetThisValue (ref).
- Let thisValue be
- Else,
- Let refEnv be ref.[[Base]].
Assert : refEnv is anEnvironment Record .- Let thisValue be refEnv.WithBaseObject().
- If
- Else,
- Let thisValue be
undefined .
- Let thisValue be
- Let argList be ?
ArgumentListEvaluation of arguments. - If func
is not an Object , throw aTypeError exception. - If
IsCallable (func) isfalse , throw aTypeError exception. - If tailPosition is
true , performPrepareForTailCall (). - Return ?
Call (func, thisValue, argList).
13.3.7 The super Keyword
13.3.7.1 Runtime Semantics: Evaluation
- Let env be
GetThisEnvironment (). - Let actualThis be ? env.GetThisBinding().
- Let propertyNameReference be ?
Evaluation ofExpression . - Let propertyNameValue be ?
GetValue (propertyNameReference). - Let strict be
IsStrict (thisSuperProperty ). - NOTE: In most cases,
ToPropertyKey will be performed on propertyNameValue immediately after this step. However, in the case ofsuper[b] = c, it will not be performed until after evaluation ofc. - Return
MakeSuperPropertyReference (actualThis, propertyNameValue, strict).
- Let env be
GetThisEnvironment (). - Let actualThis be ? env.GetThisBinding().
- Let propertyKey be the
StringValue ofIdentifierName . - Let strict be
IsStrict (thisSuperProperty ). - Return
MakeSuperPropertyReference (actualThis, propertyKey, strict).
- Let newTarget be
GetNewTarget (). Assert : newTarget is aconstructor .- Let func be
GetSuperConstructor (). - Let argList be ?
ArgumentListEvaluation ofArguments . - If
IsConstructor (func) isfalse , throw aTypeError exception. - Let result be ?
Construct (func, argList, newTarget). - Let thisER be
GetThisEnvironment (). Assert : thisER is aFunction Environment Record .- Perform ?
BindThisValue (thisER, result). - Let F be thisER.[[FunctionObject]].
Assert : F is an ECMAScriptfunction object .- Perform ?
InitializeInstanceElements (result, F). - Return result.
13.3.7.2 GetSuperConstructor ( )
The abstract operation GetSuperConstructor takes no arguments and returns an
- Let envRec be
GetThisEnvironment (). Assert : envRec is aFunction Environment Record .- Let activeFunction be envRec.[[FunctionObject]].
Assert : activeFunction is an ECMAScriptfunction object .- Let superConstructor be ! activeFunction.[[GetPrototypeOf]]().
- Return superConstructor.
13.3.7.3 MakeSuperPropertyReference ( actualThis, propertyKey, strict )
The abstract operation MakeSuperPropertyReference takes arguments actualThis (an
- Let env be
GetThisEnvironment (). Assert : env.HasSuperBinding() istrue .Assert : env is aFunction Environment Record .- Let baseValue be
GetSuperBase (env). - Return the
Reference Record { [[Base]]: baseValue, [[ReferencedName]]: propertyKey, [[Strict]]: strict, [[ThisValue]]: actualThis }.
13.3.8 Argument Lists
The evaluation of an argument list produces a
13.3.8.1 Runtime Semantics: ArgumentListEvaluation
The
- Return a new empty
List .
- Let ref be ?
Evaluation ofAssignmentExpression . - Let arg be ?
GetValue (ref). - Return « arg ».
- Let list be a new empty
List . - Let spreadRef be ?
Evaluation ofAssignmentExpression . - Let spreadObj be ?
GetValue (spreadRef). - Let iteratorRecord be ?
GetIterator (spreadObj,sync ). - Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , return list. - Append next to list.
- Let next be ?
- Let precedingArgs be ?
ArgumentListEvaluation ofArgumentList . - Let ref be ?
Evaluation ofAssignmentExpression . - Let arg be ?
GetValue (ref). - Return the
list-concatenation of precedingArgs and « arg ».
- Let precedingArgs be ?
ArgumentListEvaluation ofArgumentList . - Let spreadRef be ?
Evaluation ofAssignmentExpression . - Let iteratorRecord be ?
GetIterator (?GetValue (spreadRef),sync ). - Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , return precedingArgs. - Append next to precedingArgs.
- Let next be ?
- Let templateLiteral be this
TemplateLiteral . - Let siteObj be
GetTemplateObject (templateLiteral). - Return « siteObj ».
- Let templateLiteral be this
TemplateLiteral . - Let siteObj be
GetTemplateObject (templateLiteral). - Let remaining be ?
ArgumentListEvaluation ofSubstitutionTemplate . - Return the
list-concatenation of « siteObj » and remaining.
- Let firstSubRef be ?
Evaluation ofExpression . - Let firstSub be ?
GetValue (firstSubRef). - Let restSub be ?
SubstitutionEvaluation ofTemplateSpans . Assert : restSub is a possibly emptyList .- Return the
list-concatenation of « firstSub » and restSub.
13.3.9 Optional Chains
?..13.3.9.1 Runtime Semantics: Evaluation
- Let baseReference be ?
Evaluation ofMemberExpression . - Let baseValue be ?
GetValue (baseReference). - If baseValue is either
undefined ornull , then- Return
undefined .
- Return
- Return ?
ChainEvaluation ofOptionalChain with arguments baseValue and baseReference.
- Let baseReference be ?
Evaluation ofCallExpression . - Let baseValue be ?
GetValue (baseReference). - If baseValue is either
undefined ornull , then- Return
undefined .
- Return
- Return ?
ChainEvaluation ofOptionalChain with arguments baseValue and baseReference.
- Let baseReference be ?
Evaluation ofOptionalExpression . - Let baseValue be ?
GetValue (baseReference). - If baseValue is either
undefined ornull , then- Return
undefined .
- Return
- Return ?
ChainEvaluation ofOptionalChain with arguments baseValue and baseReference.
13.3.9.2 Runtime Semantics: ChainEvaluation
The
- Let thisChain be this
OptionalChain . - Let tailCall be
IsInTailPosition (thisChain). - Return ?
EvaluateCall (baseValue, baseReference,Arguments , tailCall).
- Let strict be
IsStrict (thisOptionalChain ). - Return ?
EvaluatePropertyAccessWithExpressionKey (baseValue,Expression , strict).
- Let strict be
IsStrict (thisOptionalChain ). - Return
EvaluatePropertyAccessWithIdentifierKey (baseValue,IdentifierName , strict).
- Let fieldNameString be the
StringValue ofPrivateIdentifier . - Return
MakePrivateReference (baseValue, fieldNameString).
- Let optionalChain be
OptionalChain . - Let newReference be ?
ChainEvaluation of optionalChain with arguments baseValue and baseReference. - Let newValue be ?
GetValue (newReference). - Let thisChain be this
OptionalChain . - Let tailCall be
IsInTailPosition (thisChain). - Return ?
EvaluateCall (newValue, newReference,Arguments , tailCall).
- Let optionalChain be
OptionalChain . - Let newReference be ?
ChainEvaluation of optionalChain with arguments baseValue and baseReference. - Let newValue be ?
GetValue (newReference). - Let strict be
IsStrict (thisOptionalChain ). - Return ?
EvaluatePropertyAccessWithExpressionKey (newValue,Expression , strict).
- Let optionalChain be
OptionalChain . - Let newReference be ?
ChainEvaluation of optionalChain with arguments baseValue and baseReference. - Let newValue be ?
GetValue (newReference). - Let strict be
IsStrict (thisOptionalChain ). - Return
EvaluatePropertyAccessWithIdentifierKey (newValue,IdentifierName , strict).
- Let optionalChain be
OptionalChain . - Let newReference be ?
ChainEvaluation of optionalChain with arguments baseValue and baseReference. - Let newValue be ?
GetValue (newReference). - Let fieldNameString be the
StringValue ofPrivateIdentifier . - Return
MakePrivateReference (newValue, fieldNameString).
13.3.10 Import Calls
13.3.10.1 Runtime Semantics: Evaluation
- Return ?
EvaluateImportCall (AssignmentExpression ).
- Return ?
EvaluateImportCall (the firstAssignmentExpression , the secondAssignmentExpression ).
13.3.10.2 EvaluateImportCall ( specifierExpression [ , optionsExpression ] )
The abstract operation EvaluateImportCall takes argument specifierExpression (a
- Let referrer be
GetActiveScriptOrModule (). - If referrer is
null , set referrer tothe current Realm Record . - Let specifierRef be ?
Evaluation of specifierExpression. - Let specifier be ?
GetValue (specifierRef). - If optionsExpression is present, then
- Let optionsRef be ?
Evaluation of optionsExpression. - Let options be ?
GetValue (optionsRef).
- Let optionsRef be ?
- Else,
- Let options be
undefined .
- Let options be
- Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let specifierString be
Completion (ToString (specifier)). IfAbruptRejectPromise (specifierString, promiseCapability).- Let attributes be a new empty
List . - If options is not
undefined , then- If options
is not an Object , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « a newly createdTypeError object »). - Return promiseCapability.[[Promise]].
- Perform !
- Let attributesObj be
Completion (Get (options,"with" )). IfAbruptRejectPromise (attributesObj, promiseCapability).- If attributesObj is not
undefined , then- If attributesObj
is not an Object , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « a newly createdTypeError object »). - Return promiseCapability.[[Promise]].
- Perform !
- Let entries be
Completion (EnumerableOwnProperties (attributesObj,key+value )). IfAbruptRejectPromise (entries, promiseCapability).- For each element entry of entries, do
- Let key be !
Get (entry,"0" ). - Let value be !
Get (entry,"1" ). - If key
is a String , then- If value
is not a String , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « a newly createdTypeError object »). - Return promiseCapability.[[Promise]].
- Perform !
- Append the
ImportAttribute Record { [[Key]]: key, [[Value]]: value } to attributes.
- If value
- Let key be !
- If attributesObj
- If
AllImportAttributesSupported (attributes) isfalse , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « a newly createdTypeError object »). - Return promiseCapability.[[Promise]].
- Perform !
- Sort attributes according to the lexicographic order of their
[[Key]] field, treating the value of each such
field as a sequence of UTF-16 code unit values. NOTE: This sorting is
observable only in that
hosts are prohibited from changing behaviour based on the order in which attributes are enumerated.
- If options
- Let moduleRequest be a new
ModuleRequest Record { [[Specifier]]: specifierString, [[Attributes]]: attributes }. - Perform
HostLoadImportedModule (referrer, moduleRequest,empty , promiseCapability). - Return promiseCapability.[[Promise]].
13.3.10.3 ContinueDynamicImport ( promiseCapability, moduleCompletion )
The abstract operation ContinueDynamicImport takes arguments promiseCapability (a
import()
- If moduleCompletion is an
abrupt completion , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « moduleCompletion.[[Value]] »). - Return
unused .
- Perform !
- Let module be moduleCompletion.[[Value]].
- Let loadPromise be module.LoadRequestedModules().
- Let rejectedClosure be a new
Abstract Closure with parameters (reason) that captures promiseCapability and performs the following steps when called:- Perform !
Call (promiseCapability.[[Reject]],undefined , « reason »). - Return
NormalCompletion (undefined ).
- Perform !
- Let onRejected be
CreateBuiltinFunction (rejectedClosure, 1,"" , « »). - Let linkAndEvaluateClosure be a new
Abstract Closure with no parameters that captures module, promiseCapability, and onRejected and performs the following steps when called:- Let link be
Completion (module.Link()). - If link is an
abrupt completion , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « link.[[Value]] »). - Return
NormalCompletion (undefined ).
- Perform !
- Let evaluatePromise be module.Evaluate().
- Let fulfilledClosure be a new
Abstract Closure with no parameters that captures module and promiseCapability and performs the following steps when called:- Let namespace be
GetModuleNamespace (module). - Perform ! Call(promiseCapability.[[Resolve]],
undefined , « namespace »). - Return
NormalCompletion (undefined ).
- Let namespace be
- Let onFulfilled be
CreateBuiltinFunction (fulfilledClosure, 0,"" , « »). - Perform
PerformPromiseThen (evaluatePromise, onFulfilled, onRejected). - Return
unused .
- Let link be
- Let linkAndEvaluate be
CreateBuiltinFunction (linkAndEvaluateClosure, 0,"" , « »). - Perform
PerformPromiseThen (loadPromise, linkAndEvaluate, onRejected). - Return
unused .
13.3.11 Tagged Templates
A tagged template is a function call where the arguments of the call are derived from a
13.3.11.1 Runtime Semantics: Evaluation
- Let tagRef be ?
Evaluation ofMemberExpression . - Let tagFunc be ?
GetValue (tagRef). - Let thisCall be this
MemberExpression . - Let tailCall be
IsInTailPosition (thisCall). - Return ?
EvaluateCall (tagFunc, tagRef,TemplateLiteral , tailCall).
- Let tagRef be ?
Evaluation ofCallExpression . - Let tagFunc be ?
GetValue (tagRef). - Let thisCall be this
CallExpression . - Let tailCall be
IsInTailPosition (thisCall). - Return ?
EvaluateCall (tagFunc, tagRef,TemplateLiteral , tailCall).
13.3.12 Meta Properties
13.3.12.1 Runtime Semantics: Evaluation
- Return
GetNewTarget ().
- Let module be
GetActiveScriptOrModule (). Assert : module is aSource Text Module Record .- Let importMeta be module.[[ImportMeta]].
- If importMeta is
empty , then- Set importMeta to
OrdinaryObjectCreate (null ). - Let importMetaValues be
HostGetImportMetaProperties (module). - For each
Record { [[Key]], [[Value]] } p of importMetaValues, do- Perform !
CreateDataPropertyOrThrow (importMeta, p.[[Key]], p.[[Value]]).
- Perform !
- Perform
HostFinalizeImportMeta (importMeta, module). - Set module.[[ImportMeta]] to importMeta.
- Return importMeta.
- Set importMeta to
- Else,
Assert : importMetais an Object .- Return importMeta.
13.3.12.1.1 HostGetImportMetaProperties ( moduleRecord )
The import.meta.
The default implementation of HostGetImportMetaProperties is to return a new empty
13.3.12.1.2 HostFinalizeImportMeta ( importMeta, moduleRecord )
The import.meta.
Most
The default implementation of HostFinalizeImportMeta is to return
13.4 Update Expressions
Syntax
13.4.1 Static Semantics: Early Errors
-
It is an early Syntax Error if the
AssignmentTargetType ofLeftHandSideExpression isinvalid .
-
It is an early Syntax Error if the
AssignmentTargetType ofUnaryExpression isinvalid .
13.4.2 Postfix Increment Operator
13.4.2.1 Runtime Semantics: Evaluation
- Let lhs be ?
Evaluation ofLeftHandSideExpression . - If the
AssignmentTargetType ofLeftHandSideExpression isweb-compat , throw aReferenceError exception. - Let oldValue be ?
ToNumeric (?GetValue (lhs)). - If oldValue
is a Number , then- Let newValue be
Number::add (oldValue,1 𝔽).
- Let newValue be
- Else,
Assert : oldValueis a BigInt .- Let newValue be
BigInt::add (oldValue,1 ℤ).
- Perform ?
PutValue (lhs, newValue). - Return oldValue.
13.4.3 Postfix Decrement Operator
13.4.3.1 Runtime Semantics: Evaluation
- Let lhs be ?
Evaluation ofLeftHandSideExpression . - If the
AssignmentTargetType ofLeftHandSideExpression isweb-compat , throw aReferenceError exception. - Let oldValue be ?
ToNumeric (?GetValue (lhs)). - If oldValue
is a Number , then- Let newValue be
Number::subtract (oldValue,1 𝔽).
- Let newValue be
- Else,
Assert : oldValueis a BigInt .- Let newValue be
BigInt::subtract (oldValue,1 ℤ).
- Perform ?
PutValue (lhs, newValue). - Return oldValue.
13.4.4 Prefix Increment Operator
13.4.4.1 Runtime Semantics: Evaluation
- Let expr be ?
Evaluation ofUnaryExpression . - If the
AssignmentTargetType ofUnaryExpression isweb-compat , throw aReferenceError exception. - Let oldValue be ?
ToNumeric (?GetValue (expr)). - If oldValue
is a Number , then- Let newValue be
Number::add (oldValue,1 𝔽).
- Let newValue be
- Else,
Assert : oldValueis a BigInt .- Let newValue be
BigInt::add (oldValue,1 ℤ).
- Perform ?
PutValue (expr, newValue). - Return newValue.
13.4.5 Prefix Decrement Operator
13.4.5.1 Runtime Semantics: Evaluation
- Let expr be ?
Evaluation ofUnaryExpression . - If the
AssignmentTargetType ofUnaryExpression isweb-compat , throw aReferenceError exception. - Let oldValue be ?
ToNumeric (?GetValue (expr)). - If oldValue
is a Number , then- Let newValue be
Number::subtract (oldValue,1 𝔽).
- Let newValue be
- Else,
Assert : oldValueis a BigInt .- Let newValue be
BigInt::subtract (oldValue,1 ℤ).
- Perform ?
PutValue (expr, newValue). - Return newValue.
13.5 Unary Operators
Syntax
13.5.1 The delete Operator
13.5.1.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsStrict (theUnaryExpression ) istrue and the derivedUnaryExpression isPrimaryExpression : IdentifierReference MemberExpression : MemberExpression . PrivateIdentifier CallExpression : CallExpression . PrivateIdentifier OptionalChain : ?. PrivateIdentifier OptionalChain : OptionalChain . PrivateIdentifier -
It is a Syntax Error if the derived
UnaryExpression is
PrimaryExpression : CoverParenthesizedExpressionAndArrowParameterList
andCoverParenthesizedExpressionAndArrowParameterList ultimately derives a phrase that, if used in place ofUnaryExpression , would produce a Syntax Error according to these rules. This rule is recursively applied.
The last rule means that expressions such as delete (((foo))) produce
13.5.1.2 Runtime Semantics: Evaluation
- Let ref be ?
Evaluation ofUnaryExpression . - If ref is not a
Reference Record , returntrue . - If
IsUnresolvableReference (ref) istrue , thenAssert : ref.[[Strict]] isfalse .- Return
true .
- If
IsPropertyReference (ref) istrue , thenAssert :IsPrivateReference (ref) isfalse .- If
IsSuperReference (ref) istrue , throw aReferenceError exception. - Let baseObj be
?
ToObject (ref.[[Base]]). - If ref.[[ReferencedName]] is not a
property key , then- Set ref.[[ReferencedName]] to
?
ToPropertyKey (ref.[[ReferencedName]]).
- Set ref.[[ReferencedName]] to
?
- Let deleteStatus be ? baseObj.[[Delete]](ref.[[ReferencedName]]).
- If deleteStatus is
false and ref.[[Strict]] istrue , throw aTypeError exception. - Return deleteStatus.
- Else,
- Let base be ref.[[Base]].
Assert : base is anEnvironment Record .- Return ? base.DeleteBinding(ref.[[ReferencedName]]).
When a delete operator occurs within delete operator occurs within
The object that may be created in step
13.5.2 The void Operator
13.5.2.1 Runtime Semantics: Evaluation
- Let expr be ?
Evaluation ofUnaryExpression . - Perform ?
GetValue (expr). - Return
undefined .
13.5.3 The typeof Operator
13.5.3.1 Runtime Semantics: Evaluation
- Let val be ?
Evaluation ofUnaryExpression . - If val is a
Reference Record , then- If
IsUnresolvableReference (val) istrue , return"undefined" .
- If
- Set val to ?
GetValue (val). - If val is
undefined , return"undefined" . - If val is
null , return"object" . - If val
is a String , return"string" . - If val
is a Symbol , return"symbol" . - If val
is a Boolean , return"boolean" . - If val
is a Number , return"number" . - If val
is a BigInt , return"bigint" . Assert : valis an Object .- NOTE: This step is replaced in section
B.3.6.3 . - If val has a [[Call]] internal method, return
"function" . - Return
"object" .
13.5.4 Unary + Operator
The unary + operator converts its operand to
13.5.4.1 Runtime Semantics: Evaluation
- Let expr be ?
Evaluation ofUnaryExpression . - Return ?
ToNumber (?GetValue (expr)).
13.5.5 Unary - Operator
The unary - operator converts its operand to a numeric value and then
negates it. Negating
13.5.5.1 Runtime Semantics: Evaluation
- Let expr be ?
Evaluation ofUnaryExpression . - Let oldValue be ?
ToNumeric (?GetValue (expr)). - If oldValue
is a Number , then- Return
Number::unaryMinus (oldValue).
- Return
- Else,
Assert : oldValueis a BigInt .- Return
BigInt::unaryMinus (oldValue).
13.5.6 Bitwise NOT Operator ( ~ )
13.5.6.1 Runtime Semantics: Evaluation
- Let expr be ?
Evaluation ofUnaryExpression . - Let oldValue be ?
ToNumeric (?GetValue (expr)). - If oldValue
is a Number , then- Return
Number::bitwiseNOT (oldValue).
- Return
- Else,
Assert : oldValueis a BigInt .- Return
BigInt::bitwiseNOT (oldValue).
13.5.7 Logical NOT Operator ( ! )
13.5.7.1 Runtime Semantics: Evaluation
- Let expr be ?
Evaluation ofUnaryExpression . - Let oldValue be
ToBoolean (?GetValue (expr)). - If oldValue is
true , returnfalse . - Return
true .
13.6 Exponentiation Operator
Syntax
13.6.1 Runtime Semantics: Evaluation
13.7 Multiplicative Operators
Syntax
- The
*operator performs multiplication, producing the product of its operands. - The
/operator performs division, producing the quotient of its operands. - The
%operator yields the remainder of its operands from an implied division.
13.7.1 Runtime Semantics: Evaluation
- Let opText be the
source text matched by MultiplicativeOperator . - Return ?
EvaluateStringOrNumericBinaryExpression (MultiplicativeExpression , opText,ExponentiationExpression ).
13.8 Additive Operators
Syntax
13.8.1 The Addition Operator ( + )
The addition operator either performs string concatenation or numeric addition.
13.8.1.1 Runtime Semantics: Evaluation
13.8.2 The Subtraction Operator ( - )
The - operator performs subtraction, producing the difference of its
operands.
13.8.2.1 Runtime Semantics: Evaluation
13.9 Bitwise Shift Operators
Syntax
13.9.1 The Left Shift Operator ( << )
Performs a bitwise left shift operation on the left operand by the amount specified by the right operand.
13.9.1.1 Runtime Semantics: Evaluation
- Return ?
EvaluateStringOrNumericBinaryExpression (ShiftExpression ,<<,AdditiveExpression ).
13.9.2 The Signed Right Shift Operator ( >> )
Performs a sign-filling bitwise right shift operation on the left operand by the amount specified by the right operand.
13.9.2.1 Runtime Semantics: Evaluation
- Return ?
EvaluateStringOrNumericBinaryExpression (ShiftExpression ,>>,AdditiveExpression ).
13.9.3 The Unsigned Right Shift Operator ( >>>
)
Performs a zero-filling bitwise right shift operation on the left operand by the amount specified by the right operand.
13.9.3.1 Runtime Semantics: Evaluation
- Return ?
EvaluateStringOrNumericBinaryExpression (ShiftExpression ,>>>,AdditiveExpression ).
13.10 Relational Operators
The result of evaluating a relational operator is always of type Boolean, reflecting whether the relationship named by the operator holds between its two operands.
Syntax
The [In] grammar parameter is needed to avoid confusing the in
operator in a relational expression with the in operator in a for
statement.
13.10.1 Runtime Semantics: Evaluation
- Let lRef be ?
Evaluation ofRelationalExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofShiftExpression . - Let rVal be ?
GetValue (rRef). - Let r be ?
IsLessThan (lVal, rVal,true ). - If r is
undefined , returnfalse ; otherwise return r.
- Let lRef be ?
Evaluation ofRelationalExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofShiftExpression . - Let rVal be ?
GetValue (rRef). - Let r be ?
IsLessThan (rVal, lVal,false ). - If r is
undefined , returnfalse ; otherwise return r.
- Let lRef be ?
Evaluation ofRelationalExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofShiftExpression . - Let rVal be ?
GetValue (rRef). - Let r be ?
IsLessThan (rVal, lVal,false ). - If r is either
true orundefined , returnfalse ; otherwise returntrue .
- Let lRef be ?
Evaluation ofRelationalExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofShiftExpression . - Let rVal be ?
GetValue (rRef). - Let r be ?
IsLessThan (lVal, rVal,true ). - If r is either
true orundefined , returnfalse ; otherwise returntrue .
- Let lRef be ?
Evaluation ofRelationalExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofShiftExpression . - Let rVal be ?
GetValue (rRef). - Return ?
InstanceofOperator (lVal, rVal).
- Let lRef be ?
Evaluation ofRelationalExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofShiftExpression . - Let rVal be ?
GetValue (rRef). - If rVal
is not an Object , throw aTypeError exception. - Return ?
HasProperty (rVal, ?ToPropertyKey (lVal)).
- Let privateIdentifier be the
StringValue ofPrivateIdentifier . - Let rRef be ?
Evaluation ofShiftExpression . - Let rVal be ?
GetValue (rRef). - If rVal
is not an Object , throw aTypeError exception. - Let privateEnv be the
running execution context 's PrivateEnvironment. Assert : privateEnv is notnull .- Let privateName be
ResolvePrivateIdentifier (privateEnv, privateIdentifier). - If
PrivateElementFind (rVal, privateName) is notempty , returntrue . - Return
false .
13.10.2 InstanceofOperator ( V, target )
The abstract operation InstanceofOperator takes arguments V (an
- If target
is not an Object , throw aTypeError exception. - Let instOfHandler be ?
GetMethod (target,%Symbol.hasInstance% ). - If instOfHandler is not
undefined , then - If
IsCallable (target) isfalse , throw aTypeError exception. - Return ?
OrdinaryHasInstance (target, V).
Steps instanceof operator semantics. If an object does not define or
inherit instanceof semantics.
13.11 Equality Operators
The result of evaluating an equality operator is always of type Boolean, reflecting whether the relationship named by the operator holds between its two operands.
Syntax
13.11.1 Runtime Semantics: Evaluation
- Let lRef be ?
Evaluation ofEqualityExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofRelationalExpression . - Let rVal be ?
GetValue (rRef). - Return ?
IsLooselyEqual (rVal, lVal).
- Let lRef be ?
Evaluation ofEqualityExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofRelationalExpression . - Let rVal be ?
GetValue (rRef). - Let r be ?
IsLooselyEqual (rVal, lVal). - If r is
true , returnfalse ; otherwise returntrue .
- Let lRef be ?
Evaluation ofEqualityExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofRelationalExpression . - Let rVal be ?
GetValue (rRef). - Return
IsStrictlyEqual (rVal, lVal).
- Let lRef be ?
Evaluation ofEqualityExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofRelationalExpression . - Let rVal be ?
GetValue (rRef). - Let r be
IsStrictlyEqual (rVal, lVal). - If r is
true , returnfalse ; otherwise returntrue .
Given the above definition of equality:
-
String comparison can be forced by:
`${a}` == `${b}`. -
Numeric comparison can be forced by:
+a == +b. -
Boolean comparison can be forced by:
!a == !b.
The equality operators maintain the following invariants:
-
A != Bis equivalent to!(A == B). -
A == Bis equivalent toB == A, except in the order of evaluation ofAandB.
The equality operator is not always transitive. For example, there might be two distinct
String objects, each representing the same String value; each String object would be
considered equal to the String value by the == operator, but the two String
objects would not be equal to each other. For example:
-
new String("a") == "a"and"a" == new String("a")are bothtrue . -
new String("a") == new String("a")isfalse .
Comparison of Strings uses a simple equality test on sequences of code unit values. There is no attempt to use the more complex, semantically oriented definitions of character or string equality and collating order defined in the Unicode specification. Therefore Strings values that are canonically equal according to the Unicode Standard could test as unequal. In effect this algorithm assumes that both Strings are already in normalized form.
13.12 Binary Bitwise Operators
Syntax
13.12.1 Runtime Semantics: Evaluation
13.13 Binary Logical Operators
Syntax
The value produced by a && or || operator is not
necessarily of type Boolean. The value produced will always be the value of one of the two
operand expressions.
13.13.1 Runtime Semantics: Evaluation
- Let lRef be ?
Evaluation ofLogicalANDExpression . - Let lVal be ?
GetValue (lRef). - If
ToBoolean (lVal) isfalse , return lVal. - Let rRef be ?
Evaluation ofBitwiseORExpression . - Return ?
GetValue (rRef).
- Let lRef be ?
Evaluation ofLogicalORExpression . - Let lVal be ?
GetValue (lRef). - If
ToBoolean (lVal) istrue , return lVal. - Let rRef be ?
Evaluation ofLogicalANDExpression . - Return ?
GetValue (rRef).
- Let lRef be ?
Evaluation ofCoalesceExpressionHead . - Let lVal be ?
GetValue (lRef). - If lVal is either
undefined ornull , then- Let rRef be ?
Evaluation ofBitwiseORExpression . - Return ?
GetValue (rRef).
- Let rRef be ?
- Else,
- Return lVal.
13.14 Conditional Operator ( ? : )
Syntax
The grammar for a
13.14.1 Runtime Semantics: Evaluation
- Let lRef be ?
Evaluation ofShortCircuitExpression . - Let lVal be
ToBoolean (?GetValue (lRef)). - If lVal is
true , then- Let trueRef be ?
Evaluation of the firstAssignmentExpression . - Return ?
GetValue (trueRef).
- Let trueRef be ?
- Else,
- Let falseRef be ?
Evaluation of the secondAssignmentExpression . - Return ?
GetValue (falseRef).
- Let falseRef be ?
13.15 Assignment Operators
Syntax
13.15.1 Static Semantics: Early Errors
-
If
LeftHandSideExpression is either anObjectLiteral or anArrayLiteral ,LeftHandSideExpression must cover anAssignmentPattern . -
If
LeftHandSideExpression is neither anObjectLiteral nor anArrayLiteral , it is a Syntax Error if theAssignmentTargetType ofLeftHandSideExpression isinvalid .
-
It is a Syntax Error if the
AssignmentTargetType ofLeftHandSideExpression isinvalid .
-
It is a Syntax Error if the
AssignmentTargetType ofLeftHandSideExpression is notsimple .
13.15.2 Runtime Semantics: Evaluation
- If
LeftHandSideExpression is neither anObjectLiteral nor anArrayLiteral , then- Let lRef be ?
Evaluation ofLeftHandSideExpression . - If the
AssignmentTargetType ofLeftHandSideExpression isweb-compat , throw aReferenceError exception. - If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue andIsIdentifierRef ofLeftHandSideExpression istrue , then- Let lhs be the
StringValue ofLeftHandSideExpression . - Let rVal be ?
NamedEvaluation ofAssignmentExpression with argument lhs.
- Let lhs be the
- Else,
- Let rRef be ?
Evaluation ofAssignmentExpression . - Let rVal be ?
GetValue (rRef).
- Let rRef be ?
- Perform
?
PutValue (lRef, rVal). - Return rVal.
- Let lRef be ?
- Let assignmentPattern be the
AssignmentPattern that iscovered byLeftHandSideExpression . - Let rRef be ?
Evaluation ofAssignmentExpression . - Let rVal be ?
GetValue (rRef). - Perform ?
DestructuringAssignmentEvaluation of assignmentPattern with argument rVal. - Return rVal.
- Let lRef be ?
Evaluation ofLeftHandSideExpression . - If the
AssignmentTargetType ofLeftHandSideExpression isweb-compat , throw aReferenceError exception. - Let lVal be
?
GetValue (lRef). - Let rRef be ?
Evaluation ofAssignmentExpression . - Let rVal be ?
GetValue (rRef). - Let assignmentOpText be the
source text matched by AssignmentOperator . - Let opText be the sequence of Unicode code points associated with
assignmentOpText in the following table:
assignmentOpText opText **=***=*/=/%=%+=+-=-<<=<<>>=>>>>>=>>>&=&^=^|=| - Let r be ?
ApplyStringOrNumericBinaryOperator (lVal, opText, rVal). - Perform ?
PutValue (lRef, r). - Return r.
- Let lRef be ?
Evaluation ofLeftHandSideExpression . - Let lVal be
?
GetValue (lRef). - If
ToBoolean (lVal) isfalse , return lVal. - If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue andIsIdentifierRef ofLeftHandSideExpression istrue , then- Let lhs be the
StringValue ofLeftHandSideExpression . - Let rVal be ?
NamedEvaluation ofAssignmentExpression with argument lhs.
- Let lhs be the
- Else,
- Let rRef be ?
Evaluation ofAssignmentExpression . - Let rVal be ?
GetValue (rRef).
- Let rRef be ?
- Perform ?
PutValue (lRef, rVal). - Return rVal.
- Let lRef be ?
Evaluation ofLeftHandSideExpression . - Let lVal be
?
GetValue (lRef). - If
ToBoolean (lVal) istrue , return lVal. - If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue andIsIdentifierRef ofLeftHandSideExpression istrue , then- Let lhs be the
StringValue ofLeftHandSideExpression . - Let rVal be ?
NamedEvaluation ofAssignmentExpression with argument lhs.
- Let lhs be the
- Else,
- Let rRef be ?
Evaluation ofAssignmentExpression . - Let rVal be ?
GetValue (rRef).
- Let rRef be ?
- Perform ?
PutValue (lRef, rVal). - Return rVal.
- Let lRef be ?
Evaluation ofLeftHandSideExpression . - Let lVal be
?
GetValue (lRef). - If lVal is neither
undefined nornull , return lVal. - If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue andIsIdentifierRef ofLeftHandSideExpression istrue , then- Let lhs be the
StringValue ofLeftHandSideExpression . - Let rVal be ?
NamedEvaluation ofAssignmentExpression with argument lhs.
- Let lhs be the
- Else,
- Let rRef be ?
Evaluation ofAssignmentExpression . - Let rVal be ?
GetValue (rRef).
- Let rRef be ?
- Perform ?
PutValue (lRef, rVal). - Return rVal.
When this expression occurs within
13.15.3 ApplyStringOrNumericBinaryOperator ( lVal, opText, rVal )
The abstract operation ApplyStringOrNumericBinaryOperator takes arguments lVal (an
**, *, /, %,
+, -, <<, >>,
>>>, &, ^, or |), and
rVal (an
- If opText is
+, then- Let lPrim be ?
ToPrimitive (lVal). - Let rPrim be ?
ToPrimitive (rVal). - If lPrim
is a String or rPrimis a String , then- Let lStr be ?
ToString (lPrim). - Let rStr be ?
ToString (rPrim). - Return the
string-concatenation of lStr and rStr.
- Let lStr be ?
- Set lVal to lPrim.
- Set rVal to rPrim.
- Let lPrim be ?
- NOTE: At this point, it must be a numeric operation.
- Let lNum be ?
ToNumeric (lVal). - Let rNum be ?
ToNumeric (rVal). - If
SameType (lNum, rNum) isfalse , throw aTypeError exception. - If lNum
is a BigInt , then- If opText is
**, return ?BigInt::exponentiate (lNum, rNum). - If opText is
/, return ?BigInt::divide (lNum, rNum). - If opText is
%, return ?BigInt::remainder (lNum, rNum). - If opText is
>>>, return ?BigInt::unsignedRightShift (lNum, rNum). - Let operation be the abstract operation associated with
opText in the following table:
opText operation *BigInt::multiply +BigInt::add -BigInt::subtract <<BigInt::leftShift >>BigInt::signedRightShift &BigInt::bitwiseAND ^BigInt::bitwiseXOR |BigInt::bitwiseOR
- If opText is
- Else,
Assert : lNumis a Number .- Let operation be the abstract operation associated with
opText in the following table:
opText operation **Number::exponentiate *Number::multiply /Number::divide %Number::remainder +Number::add -Number::subtract <<Number::leftShift >>Number::signedRightShift >>>Number::unsignedRightShift &Number::bitwiseAND ^Number::bitwiseXOR |Number::bitwiseOR
- Return operation(lNum, rNum).
No hint is provided in the calls to
Step
13.15.4 EvaluateStringOrNumericBinaryExpression ( leftOperand, opText, rightOperand )
The abstract operation EvaluateStringOrNumericBinaryExpression takes arguments
leftOperand (a
- Let lRef be ?
Evaluation of leftOperand. - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation of rightOperand. - Let rVal be ?
GetValue (rRef). - Return ?
ApplyStringOrNumericBinaryOperator (lVal, opText, rVal).
13.15.5 Destructuring Assignment
Supplemental Syntax
In certain circumstances when processing an instance of the production
the interpretation of
13.15.5.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
AssignmentTargetType ofIdentifierReference is notsimple .
-
It is a Syntax Error if
DestructuringAssignmentTarget is either anArrayLiteral or anObjectLiteral .
-
If
LeftHandSideExpression is either anObjectLiteral or anArrayLiteral ,LeftHandSideExpression must cover anAssignmentPattern . -
If
LeftHandSideExpression is neither anObjectLiteral nor anArrayLiteral , it is a Syntax Error if theAssignmentTargetType ofLeftHandSideExpression is notsimple .
13.15.5.2 Runtime Semantics: DestructuringAssignmentEvaluation
The
- Perform ?
RequireObjectCoercible (value). - Return
unused .
- Perform ?
RequireObjectCoercible (value). - Perform ?
PropertyDestructuringAssignmentEvaluation ofAssignmentPropertyList with argument value. - Return
unused .
- Perform ?
RequireObjectCoercible (value). - Let excludedNames be a new empty
List . - Return ?
RestDestructuringAssignmentEvaluation ofAssignmentRestProperty with arguments value and excludedNames.
- Perform ?
RequireObjectCoercible (value). - Let excludedNames be ?
PropertyDestructuringAssignmentEvaluation ofAssignmentPropertyList with argument value. - Return ?
RestDestructuringAssignmentEvaluation ofAssignmentRestProperty with arguments value and excludedNames.
- Let iteratorRecord be ?
GetIterator (value,sync ). - Return ?
IteratorClose (iteratorRecord,NormalCompletion (unused )).
- Let iteratorRecord be ?
GetIterator (value,sync ). - Let result be
Completion (IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord). - If iteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord, result). - Return result.
- Let iteratorRecord be ?
GetIterator (value,sync ). - If
Elision is present, then- Let status be
Completion (IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord). - If status is an
abrupt completion , thenAssert : iteratorRecord.[[Done]] istrue .- Return ? status.
- Let status be
- Let result be
Completion (IteratorDestructuringAssignmentEvaluation ofAssignmentRestElement with argument iteratorRecord). - If iteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord, result). - Return result.
- Let iteratorRecord be ?
GetIterator (value,sync ). - Let result be
Completion (IteratorDestructuringAssignmentEvaluation ofAssignmentElementList with argument iteratorRecord). - If iteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord, result). - Return result.
- Let iteratorRecord be ?
GetIterator (value,sync ). - Let status be
Completion (IteratorDestructuringAssignmentEvaluation ofAssignmentElementList with argument iteratorRecord). - If status is an
abrupt completion , then- If iteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord, status). - Return ? status.
- If iteratorRecord.[[Done]] is
- If
Elision is present, then- Set status to
Completion (IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord). - If status is an
abrupt completion , thenAssert : iteratorRecord.[[Done]] istrue .- Return ? status.
- Set status to
- If
AssignmentRestElement is present, then- Set status to
Completion (IteratorDestructuringAssignmentEvaluation ofAssignmentRestElement with argument iteratorRecord).
- Set status to
- If iteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord, status). - Return ? status.
13.15.5.3 Runtime Semantics: PropertyDestructuringAssignmentEvaluation
The
- Let propertyNames be ?
PropertyDestructuringAssignmentEvaluation ofAssignmentPropertyList with argument value. - Let nextNames be ?
PropertyDestructuringAssignmentEvaluation ofAssignmentProperty with argument value. - Return the
list-concatenation of propertyNames and nextNames.
- Let P be the
StringValue ofIdentifierReference . - Let lRef be ?
ResolveBinding (P). - Let v be ?
GetV (value, P). - If
Initializer is present and v isundefined , then- If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Set v to ?
NamedEvaluation ofInitializer with argument P.
- Set v to ?
- Else,
- Let defaultValue be ?
Evaluation ofInitializer . - Set v to ?
GetValue (defaultValue).
- Let defaultValue be ?
- If
- Perform ?
PutValue (lRef, v). - Return « P ».
- Let name be ?
Evaluation ofPropertyName . - Perform ?
KeyedDestructuringAssignmentEvaluation ofAssignmentElement with arguments value and name. - Return « name ».
13.15.5.4 Runtime Semantics: RestDestructuringAssignmentEvaluation
The
- Let lRef be ?
Evaluation ofDestructuringAssignmentTarget . - Let restObj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform ?
CopyDataProperties (restObj, value, excludedNames). - Return ?
PutValue (lRef, restObj).
13.15.5.5 Runtime Semantics: IteratorDestructuringAssignmentEvaluation
The
- Return ?
IteratorDestructuringAssignmentEvaluation ofAssignmentElisionElement with argument iteratorRecord.
- Perform ?
IteratorDestructuringAssignmentEvaluation ofAssignmentElementList with argument iteratorRecord. - Return ?
IteratorDestructuringAssignmentEvaluation ofAssignmentElisionElement with argument iteratorRecord.
- Return ?
IteratorDestructuringAssignmentEvaluation ofAssignmentElement with argument iteratorRecord.
- Perform ?
IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord. - Return ?
IteratorDestructuringAssignmentEvaluation ofAssignmentElement with argument iteratorRecord.
- If iteratorRecord.[[Done]] is
false , then- Perform ?
IteratorStep (iteratorRecord).
- Perform ?
- Return
unused .
- Perform ?
IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord. - If iteratorRecord.[[Done]] is
false , then- Perform ?
IteratorStep (iteratorRecord).
- Perform ?
- Return
unused .
- If
DestructuringAssignmentTarget is neither anObjectLiteral nor anArrayLiteral , then- Let lRef be ?
Evaluation ofDestructuringAssignmentTarget .
- Let lRef be ?
- Let value be
undefined . - If iteratorRecord.[[Done]] is
false , then- Let next be ?
IteratorStepValue (iteratorRecord). - If next is not
done , then- Set value to next.
- Let next be ?
- If
Initializer is present and value isundefined , then- If
IsAnonymousFunctionDefinition (Initializer ) istrue andIsIdentifierRef ofDestructuringAssignmentTarget istrue , then- Let target be the
StringValue ofDestructuringAssignmentTarget . - Let v be ?
NamedEvaluation ofInitializer with argument target.
- Let target be the
- Else,
- Let defaultValue be ?
Evaluation ofInitializer . - Let v be ?
GetValue (defaultValue).
- Let defaultValue be ?
- If
- Else,
- Let v be value.
- If
DestructuringAssignmentTarget is either anObjectLiteral or anArrayLiteral , then- Let nestedAssignmentPattern be the
AssignmentPattern that iscovered byDestructuringAssignmentTarget . - Return ?
DestructuringAssignmentEvaluation of nestedAssignmentPattern with argument v.
- Let nestedAssignmentPattern be the
- Return ?
PutValue (lRef, v).
Left to right evaluation order is maintained by evaluating a
- If
DestructuringAssignmentTarget is neither anObjectLiteral nor anArrayLiteral , then- Let lRef be ?
Evaluation ofDestructuringAssignmentTarget .
- Let lRef be ?
- Let A be !
ArrayCreate (0). - Let n be 0.
- Repeat, while iteratorRecord.[[Done]] is
false ,- Let next be ?
IteratorStepValue (iteratorRecord). - If next is not
done , then- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), next). - Set n to n + 1.
- Perform !
- Let next be ?
- If
DestructuringAssignmentTarget is neither anObjectLiteral nor anArrayLiteral , then- Return ?
PutValue (lRef, A).
- Return ?
- Let nestedAssignmentPattern be the
AssignmentPattern that iscovered byDestructuringAssignmentTarget . - Return ?
DestructuringAssignmentEvaluation of nestedAssignmentPattern with argument A.
13.15.5.6 Runtime Semantics: KeyedDestructuringAssignmentEvaluation
The
- If
DestructuringAssignmentTarget is neither anObjectLiteral nor anArrayLiteral , then- Let lRef be ?
Evaluation ofDestructuringAssignmentTarget .
- Let lRef be ?
- Let v be ?
GetV (value, propertyName). - If
Initializer is present and v isundefined , then- If
IsAnonymousFunctionDefinition (Initializer ) istrue andIsIdentifierRef ofDestructuringAssignmentTarget istrue , then- Let target be the
StringValue ofDestructuringAssignmentTarget . - Let rhsValue be ?
NamedEvaluation ofInitializer with argument target.
- Let target be the
- Else,
- Let defaultValue be ?
Evaluation ofInitializer . - Let rhsValue be ?
GetValue (defaultValue).
- Let defaultValue be ?
- If
- Else,
- Let rhsValue be v.
- If
DestructuringAssignmentTarget is either anObjectLiteral or anArrayLiteral , then- Let assignmentPattern be the
AssignmentPattern that iscovered byDestructuringAssignmentTarget . - Return ?
DestructuringAssignmentEvaluation of assignmentPattern with argument rhsValue.
- Let assignmentPattern be the
- Return ?
PutValue (lRef, rhsValue).
13.16 Comma Operator ( , )
Syntax
13.16.1 Runtime Semantics: Evaluation
- Let lRef be ?
Evaluation ofExpression . - Perform ?
GetValue (lRef). - Let rRef be ?
Evaluation ofAssignmentExpression . - Return ?
GetValue (rRef).
14 ECMAScript Language: Statements and Declarations
Syntax
14.1 Statement Semantics
14.1.1 Runtime Semantics: Evaluation
- Return
empty .
- Return ?
Evaluation ofFunctionDeclaration .
- Let newLabelSet be a new empty
List . - Return ?
LabelledEvaluation of thisBreakableStatement with argument newLabelSet.
14.2 Block
Syntax
14.2.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
LexicallyDeclaredNames ofStatementList contains any duplicate entries. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofStatementList also occurs in theVarDeclaredNames ofStatementList .
14.2.2 Runtime Semantics: Evaluation
- Return
empty .
- Let oldEnv be the
running execution context 's LexicalEnvironment. - Let blockEnv be
NewDeclarativeEnvironment (oldEnv). - Perform
BlockDeclarationInstantiation (StatementList , blockEnv). - Set the
running execution context 's LexicalEnvironment to blockEnv. - Let blockValue be
Completion (Evaluation ofStatementList ). - Set the
running execution context 's LexicalEnvironment to oldEnv. - Return ? blockValue.
No matter how control leaves the
- Let sl be ?
Evaluation ofStatementList . - Let s be
Completion (Evaluation ofStatementListItem ). - Return ?
UpdateEmpty (s, sl).
The value of a eval function all return the value 1:
eval("1;;;;;")
eval("1;{}")
eval("1;var a;")14.2.3 BlockDeclarationInstantiation ( code, env )
The abstract operation BlockDeclarationInstantiation takes arguments code (a
When a
It performs the following steps when called:
- Let declarations be the
LexicallyScopedDeclarations of code. - Let privateEnv be the
running execution context 's PrivateEnvironment. - For each element d of declarations, do
- For each element dn of the
BoundNames of d, do- If
IsConstantDeclaration of d istrue , then- Perform
! env.CreateImmutableBinding(dn,
true ).
- Perform
! env.CreateImmutableBinding(dn,
- Else,
-
Perform
! env.CreateMutableBinding(dn,
false ). NOTE: This step is replaced in sectionB.3.2.6 .
-
Perform
! env.CreateMutableBinding(dn,
- If
- If d is either a
FunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration , then- Let fn be the sole element of the
BoundNames of d. - Let fo be
InstantiateFunctionObject of d with arguments env and privateEnv. - Perform
! env.InitializeBinding(fn, fo).
NOTE: This step is replaced in section
B.3.2.6 .
- Let fn be the sole element of the
- For each element dn of the
- Return
unused .
14.3 Declarations and the Variable Statement
14.3.1 Let and Const Declarations
let and const declarations define variables that are scoped to
the let
declaration does not have an
Syntax
14.3.1.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
BoundNames ofBindingList contains"let" . -
It is a Syntax Error if the
BoundNames ofBindingList contains any duplicate entries.
-
It is a Syntax Error if
Initializer is not present andIsConstantDeclaration of theLexicalDeclaration containing thisLexicalBinding istrue .
14.3.1.2 Runtime Semantics: Evaluation
- Perform ?
Evaluation ofBindingList . - Return
empty .
- Perform ?
Evaluation ofBindingList . - Return ?
Evaluation ofLexicalBinding .
- Let lhs be !
ResolveBinding (StringValue ofBindingIdentifier ). - Perform !
InitializeReferencedBinding (lhs,undefined ). - Return
empty .
A const declaration.
- Let bindingId be the
StringValue ofBindingIdentifier . - Let lhs be !
ResolveBinding (bindingId). - If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Let value be ?
NamedEvaluation ofInitializer with argument bindingId.
- Let value be ?
- Else,
- Let rhs be ?
Evaluation ofInitializer . - Let value be ?
GetValue (rhs).
- Let rhs be ?
- Perform !
InitializeReferencedBinding (lhs, value). - Return
empty .
- Let rhs be ?
Evaluation ofInitializer . - Let value be ?
GetValue (rhs). - Let env be the
running execution context 's LexicalEnvironment. - Return ?
BindingInitialization ofBindingPattern with arguments value and env.
14.3.2 Variable Statement
A var statement declares variables that are scoped to the
Syntax
14.3.2.1 Runtime Semantics: Evaluation
- Perform ?
Evaluation ofVariableDeclarationList . - Return
empty .
- Perform ?
Evaluation ofVariableDeclarationList . - Return ?
Evaluation ofVariableDeclaration .
- Return
empty .
- Let bindingId be the
StringValue ofBindingIdentifier . - Let lhs be ?
ResolveBinding (bindingId). - If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Let value be ?
NamedEvaluation ofInitializer with argument bindingId.
- Let value be ?
- Else,
- Let rhs be ?
Evaluation ofInitializer . - Let value be ?
GetValue (rhs).
- Let rhs be ?
- Perform ?
PutValue (lhs, value). - Return
empty .
If a
- Let rhs be ?
Evaluation ofInitializer . - Let rVal be ?
GetValue (rhs). - Return ?
BindingInitialization ofBindingPattern with arguments rVal andundefined .
14.3.3 Destructuring Binding Patterns
Syntax
14.3.3.1 Runtime Semantics: PropertyBindingInitialization
The
- Let boundNames be ?
PropertyBindingInitialization ofBindingPropertyList with arguments value and environment. - Let nextNames be ?
PropertyBindingInitialization ofBindingProperty with arguments value and environment. - Return the
list-concatenation of boundNames and nextNames.
- Let name be the sole element of the
BoundNames ofSingleNameBinding . - Perform ?
KeyedBindingInitialization ofSingleNameBinding with arguments value, environment, and name. - Return « name ».
- Let P be ?
Evaluation ofPropertyName . - Perform ?
KeyedBindingInitialization ofBindingElement with arguments value, environment, and P. - Return « P ».
14.3.3.2 Runtime Semantics: RestBindingInitialization
The
- Let lhs be ?
ResolveBinding (StringValue ofBindingIdentifier , environment). - Let restObj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform ?
CopyDataProperties (restObj, value, excludedNames). - If environment is
undefined , return ?PutValue (lhs, restObj). - Return ?
InitializeReferencedBinding (lhs, restObj).
14.3.3.3 Runtime Semantics: KeyedBindingInitialization
The
When
It is defined piecewise over the following productions:
- Let v be ?
GetV (value, propertyName). - If
Initializer is present and v isundefined , then- Let defaultValue be ?
Evaluation ofInitializer . - Set v to ?
GetValue (defaultValue).
- Let defaultValue be ?
- Return ?
BindingInitialization ofBindingPattern with arguments v and environment.
- Let bindingId be the
StringValue ofBindingIdentifier . - Let lhs be ?
ResolveBinding (bindingId, environment). - Let v be ?
GetV (value, propertyName). - If
Initializer is present and v isundefined , then- If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Set v to ?
NamedEvaluation ofInitializer with argument bindingId.
- Set v to ?
- Else,
- Let defaultValue be ?
Evaluation ofInitializer . - Set v to ?
GetValue (defaultValue).
- Let defaultValue be ?
- If
- If environment is
undefined , return ?PutValue (lhs, v). - Return ?
InitializeReferencedBinding (lhs, v).
14.4 Empty Statement
Syntax
14.4.1 Runtime Semantics: Evaluation
- Return
empty .
14.5 Expression Statement
Syntax
An function or class async function because that would make it ambiguous with an let [ because that would make it
ambiguous with a let
14.5.1 Runtime Semantics: Evaluation
- Let exprRef be ?
Evaluation ofExpression . - Return ?
GetValue (exprRef).
14.6 The if Statement
Syntax
else] resolves the
classic "dangling else" problem in the usual way. That is, when the choice of associated
if is otherwise ambiguous, the else is associated with the nearest
(innermost) of the candidate ifs
14.6.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsLabelledFunction (the firstStatement ) istrue . -
It is a Syntax Error if
IsLabelledFunction (the secondStatement ) istrue .
-
It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply this rule if the extension specified in
14.6.2 Runtime Semantics: Evaluation
- Let exprRef be ?
Evaluation ofExpression . - Let exprValue be
ToBoolean (?GetValue (exprRef)). - If exprValue is
true , then- Let stmtCompletion be
Completion (Evaluation of the firstStatement ).
- Let stmtCompletion be
- Else,
- Let stmtCompletion be
Completion (Evaluation of the secondStatement ).
- Let stmtCompletion be
- Return ?
UpdateEmpty (stmtCompletion,undefined ).
- Let exprRef be ?
Evaluation ofExpression . - Let exprValue be
ToBoolean (?GetValue (exprRef)). - If exprValue is
false , then- Return
undefined .
- Return
- Else,
- Let stmtCompletion be
Completion (Evaluation ofStatement ). - Return ?
UpdateEmpty (stmtCompletion,undefined ).
- Let stmtCompletion be
14.7 Iteration Statements
Syntax
14.7.1 Semantics
14.7.1.1 LoopContinues ( completion, labelSet )
The abstract operation LoopContinues takes arguments completion (a
- If completion is a
normal completion , returntrue . - If completion is not a
continue completion , returnfalse . - If completion.[[Target]] is
empty , returntrue . - If labelSet contains completion.[[Target]], return
true . - Return
false .
Within the
14.7.1.2 Runtime Semantics: LoopEvaluation
The
- Return ?
DoWhileLoopEvaluation ofDoWhileStatement with argument labelSet.
- Return ?
WhileLoopEvaluation ofWhileStatement with argument labelSet.
- Return ?
ForLoopEvaluation ofForStatement with argument labelSet.
- Return ?
ForInOfLoopEvaluation ofForInOfStatement with argument labelSet.
14.7.2 The do-while Statement
Syntax
14.7.2.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply this rule if the extension specified in
14.7.2.2 Runtime Semantics: DoWhileLoopEvaluation
The
- Let V be
undefined . - Repeat,
- Let stmtResult be
Completion (Evaluation ofStatement ). - If
LoopContinues (stmtResult, labelSet) isfalse , return ?UpdateEmpty (stmtResult, V). - If stmtResult.[[Value]] is not
empty , set V to stmtResult.[[Value]]. - Let exprRef be ?
Evaluation ofExpression . - Let exprValue be ?
GetValue (exprRef). - If
ToBoolean (exprValue) isfalse , return V.
- Let stmtResult be
14.7.3 The while Statement
Syntax
14.7.3.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply this rule if the extension specified in
14.7.3.2 Runtime Semantics: WhileLoopEvaluation
The
- Let V be
undefined . - Repeat,
- Let exprRef be ?
Evaluation ofExpression . - Let exprValue be ?
GetValue (exprRef). - If
ToBoolean (exprValue) isfalse , return V. - Let stmtResult be
Completion (Evaluation ofStatement ). - If
LoopContinues (stmtResult, labelSet) isfalse , return ?UpdateEmpty (stmtResult, V). - If stmtResult.[[Value]] is not
empty , set V to stmtResult.[[Value]].
- Let exprRef be ?
14.7.4 The for Statement
Syntax
14.7.4.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply this rule if the extension specified in
-
It is a Syntax Error if any element of the
BoundNames ofLexicalDeclaration also occurs in theVarDeclaredNames ofStatement .
14.7.4.2 Runtime Semantics: ForLoopEvaluation
The
- If the first
Expression is present, then- Let exprRef be ?
Evaluation of the firstExpression . - Perform ?
GetValue (exprRef).
- Let exprRef be ?
- If the second
Expression is present, let test be the secondExpression ; otherwise let test beempty . - If the third
Expression is present, let increment be the thirdExpression ; otherwise let increment beempty . - Return ?
ForBodyEvaluation (test, increment,Statement , « », labelSet).
- Perform ?
Evaluation ofVariableDeclarationList . - If the first
Expression is present, let test be the firstExpression ; otherwise let test beempty . - If the second
Expression is present, let increment be the secondExpression ; otherwise let increment beempty . - Return ?
ForBodyEvaluation (test, increment,Statement , « », labelSet).
- Let oldEnv be the
running execution context 's LexicalEnvironment. - Let loopEnv be
NewDeclarativeEnvironment (oldEnv). - Let isConst be
IsConstantDeclaration ofLexicalDeclaration . - Let boundNames be the
BoundNames ofLexicalDeclaration . - For each element dn of boundNames, do
- If isConst is
true , then- Perform
! loopEnv.CreateImmutableBinding(dn,
true ).
- Perform
! loopEnv.CreateImmutableBinding(dn,
- Else,
- Perform
! loopEnv.CreateMutableBinding(dn,
false ).
- Perform
! loopEnv.CreateMutableBinding(dn,
- If isConst is
- Set the
running execution context 's LexicalEnvironment to loopEnv. - Let forDcl be
Completion (Evaluation ofLexicalDeclaration ). - If forDcl is an
abrupt completion , then- Set the
running execution context 's LexicalEnvironment to oldEnv. - Return ? forDcl.
- Set the
- If isConst is
false , let perIterationLets be boundNames; otherwise let perIterationLets be a new emptyList . - If the first
Expression is present, let test be the firstExpression ; otherwise let test beempty . - If the second
Expression is present, let increment be the secondExpression ; otherwise let increment beempty . - Let bodyResult be
Completion (ForBodyEvaluation (test, increment,Statement , perIterationLets, labelSet)). - Set the
running execution context 's LexicalEnvironment to oldEnv. - Return ? bodyResult.
14.7.4.3 ForBodyEvaluation ( test, increment, stmt, perIterationBindings, labelSet )
The abstract operation ForBodyEvaluation takes arguments test (an
- Let V be
undefined . - Perform ?
CreatePerIterationEnvironment (perIterationBindings). - Repeat,
- If test is not
empty , then- Let testRef be ?
Evaluation of test. - Let testValue be ?
GetValue (testRef). - If
ToBoolean (testValue) isfalse , return V.
- Let testRef be ?
- Let result be
Completion (Evaluation of stmt). - If
LoopContinues (result, labelSet) isfalse , return ?UpdateEmpty (result, V). - If result.[[Value]] is not
empty , set V to result.[[Value]]. - Perform ?
CreatePerIterationEnvironment (perIterationBindings). - If increment is not
empty , then- Let incRef be ?
Evaluation of increment. - Perform ?
GetValue (incRef).
- Let incRef be ?
- If test is not
14.7.4.4 CreatePerIterationEnvironment ( perIterationBindings )
The abstract operation CreatePerIterationEnvironment takes argument
perIterationBindings (a
- If perIterationBindings has any elements, then
- Let lastIterationEnv be the
running execution context 's LexicalEnvironment. - Let outer be lastIterationEnv.[[OuterEnv]].
Assert : outer is notnull .- Let thisIterationEnv be
NewDeclarativeEnvironment (outer). - For each element bn of perIterationBindings, do
- Perform
! thisIterationEnv.CreateMutableBinding(bn,
false ). - Let lastValue be
? lastIterationEnv.GetBindingValue(bn,
true ). - Perform ! thisIterationEnv.InitializeBinding(bn, lastValue).
- Perform
! thisIterationEnv.CreateMutableBinding(bn,
- Set the
running execution context 's LexicalEnvironment to thisIterationEnv.
- Let lastIterationEnv be the
- Return
unused .
14.7.5 The for-in,
for-of, and for-await-of
Statements
Syntax
This section is extended by Annex
14.7.5.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply this rule if the extension specified in
-
If
LeftHandSideExpression is either anObjectLiteral or anArrayLiteral ,LeftHandSideExpression must cover anAssignmentPattern . -
If
LeftHandSideExpression is neither anObjectLiteral nor anArrayLiteral , it is a Syntax Error if theAssignmentTargetType ofLeftHandSideExpression isinvalid .
-
It is a Syntax Error if the
BoundNames ofForDeclaration contains"let" . -
It is a Syntax Error if any element of the
BoundNames ofForDeclaration also occurs in theVarDeclaredNames ofStatement . -
It is a Syntax Error if the
BoundNames ofForDeclaration contains any duplicate entries.
14.7.5.2 Static Semantics: IsDestructuring
The
- If
PrimaryExpression is either anObjectLiteral or anArrayLiteral , returntrue . - Return
false .
- Return
false .
- Return
IsDestructuring ofForBinding .
- Return
false .
- Return
true .
This section is extended by Annex
14.7.5.3 Runtime Semantics: ForDeclarationBindingInitialization
The
var statements
and the formal parameter lists of some
It is defined piecewise over the following productions:
- Return ?
BindingInitialization ofForBinding with arguments value and environment.
14.7.5.4 Runtime Semantics: ForDeclarationBindingInstantiation
The
- For each element name of the
BoundNames ofForBinding , do- If
IsConstantDeclaration ofLetOrConst istrue , then- Perform
! environment.CreateImmutableBinding(name,
true ).
- Perform
! environment.CreateImmutableBinding(name,
- Else,
- Perform
! environment.CreateMutableBinding(name,
false ).
- Perform
! environment.CreateMutableBinding(name,
- If
- Return
unused .
14.7.5.5 Runtime Semantics: ForInOfLoopEvaluation
The
- Let keyResult be ?
ForIn/OfHeadEvaluation (« »,Expression ,enumerate ). - Return ?
ForIn/OfBodyEvaluation (LeftHandSideExpression ,Statement , keyResult,enumerate ,assignment , labelSet).
- Let keyResult be ?
ForIn/OfHeadEvaluation (« »,Expression ,enumerate ). - Return ?
ForIn/OfBodyEvaluation (ForBinding ,Statement , keyResult,enumerate ,var-binding , labelSet).
- Let keyResult be ?
ForIn/OfHeadEvaluation (BoundNames ofForDeclaration ,Expression ,enumerate ). - Return ?
ForIn/OfBodyEvaluation (ForDeclaration ,Statement , keyResult,enumerate ,lexical-binding , labelSet).
- Let keyResult be ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,iterate ). - Return ?
ForIn/OfBodyEvaluation (LeftHandSideExpression ,Statement , keyResult,iterate ,assignment , labelSet).
- Let keyResult be ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,iterate ). - Return ?
ForIn/OfBodyEvaluation (ForBinding ,Statement , keyResult,iterate ,var-binding , labelSet).
- Let keyResult be ?
ForIn/OfHeadEvaluation (BoundNames ofForDeclaration ,AssignmentExpression ,iterate ). - Return ?
ForIn/OfBodyEvaluation (ForDeclaration ,Statement , keyResult,iterate ,lexical-binding , labelSet).
- Let keyResult be ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,async-iterate ). - Return ?
ForIn/OfBodyEvaluation (LeftHandSideExpression ,Statement , keyResult,iterate ,assignment , labelSet,async ).
- Let keyResult be ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,async-iterate ). - Return ?
ForIn/OfBodyEvaluation (ForBinding ,Statement , keyResult,iterate ,var-binding , labelSet,async ).
- Let keyResult be ?
ForIn/OfHeadEvaluation (BoundNames ofForDeclaration ,AssignmentExpression ,async-iterate ). - Return ?
ForIn/OfBodyEvaluation (ForDeclaration ,Statement , keyResult,iterate ,lexical-binding , labelSet,async ).
This section is extended by Annex
14.7.5.6 ForIn/OfHeadEvaluation ( uninitializedBoundNames, expr, iterationKind )
The abstract operation ForIn/OfHeadEvaluation takes arguments
uninitializedBoundNames (a
- Let oldEnv be the
running execution context 's LexicalEnvironment. - If uninitializedBoundNames is not empty, then
Assert : uninitializedBoundNames has no duplicate entries.- Let newEnv be
NewDeclarativeEnvironment (oldEnv). - For each String name of uninitializedBoundNames, do
- Perform
! newEnv.CreateMutableBinding(name,
false ).
- Perform
! newEnv.CreateMutableBinding(name,
- Set the
running execution context 's LexicalEnvironment to newEnv.
- Let exprRef be
Completion (Evaluation of expr). - Set the
running execution context 's LexicalEnvironment to oldEnv. - Let exprValue be ?
GetValue (? exprRef). - If iterationKind is
enumerate , then- If exprValue is either
undefined ornull , then- Return
Completion Record { [[Type]]:break , [[Value]]:empty , [[Target]]:empty }.
- Return
- Let obj be !
ToObject (exprValue). - Let iterator be
EnumerateObjectProperties (obj). - Let nextMethod be !
GetV (iterator,"next" ). - Return the
Iterator Record { [[Iterator]]: iterator, [[NextMethod]]: nextMethod, [[Done]]:false }.
- If exprValue is either
- Else,
Assert : iterationKind is eitheriterate orasync-iterate .- If iterationKind is
async-iterate , let iteratorKind beasync . - Else, let iteratorKind be
sync . - Return ?
GetIterator (exprValue, iteratorKind).
14.7.5.7 ForIn/OfBodyEvaluation ( lhs, stmt, iteratorRecord, iterationKind, lhsKind, labelSet [ , iteratorKind ] )
The abstract operation ForIn/OfBodyEvaluation takes arguments lhs (a
- If iteratorKind is not present, set iteratorKind to
sync . - Let oldEnv be the
running execution context 's LexicalEnvironment. - Let V be
undefined . - Let destructuring be
IsDestructuring of lhs. - If destructuring is
true and lhsKind isassignment , thenAssert : lhs is aLeftHandSideExpression .- Let assignmentPattern be the
AssignmentPattern that iscovered by lhs.
- Repeat,
- Let nextResult be ?
Call (iteratorRecord.[[NextMethod]], iteratorRecord.[[Iterator]]). - If iteratorKind is
async , set nextResult to ?Await (nextResult). - If nextResult
is not an Object , throw aTypeError exception. - Let done be ?
IteratorComplete (nextResult). - If done is
true , return V. - Let nextValue be ?
IteratorValue (nextResult). - If lhsKind is either
assignment orvar-binding , then- If destructuring is
true , then- If lhsKind is
assignment , then- Let status be
Completion (DestructuringAssignmentEvaluation of assignmentPattern with argument nextValue).
- Let status be
- Else,
Assert : lhsKind isvar-binding .Assert : lhs is aForBinding .- Let status be
Completion (BindingInitialization of lhs with arguments nextValue andundefined ).
- If lhsKind is
- Else,
- Let lhsRef be
Completion (Evaluation of lhs). (It may be evaluated repeatedly.) - If lhsKind is
assignment and theAssignmentTargetType of lhs isweb-compat , throw aReferenceError exception. - If lhsRef is an
abrupt completion , then- Let status be lhsRef.
- Else,
- Let status be
Completion (PutValue (lhsRef.[[Value]], nextValue)).
- Let status be
- Let lhsRef be
- If destructuring is
- Else,
Assert : lhsKind islexical-binding .Assert : lhs is aForDeclaration .- Let iterationEnv be
NewDeclarativeEnvironment (oldEnv). - Perform
ForDeclarationBindingInstantiation of lhs with argument iterationEnv. - Set the
running execution context 's LexicalEnvironment to iterationEnv. - If destructuring is
true , then- Let status be
Completion (ForDeclarationBindingInitialization of lhs with arguments nextValue and iterationEnv).
- Let status be
- Else,
Assert : lhs binds a single name.- Let lhsName be the sole element of the
BoundNames of lhs. - Let lhsRef be !
ResolveBinding (lhsName). - Let status be
Completion (InitializeReferencedBinding (lhsRef, nextValue)).
- If status is an
abrupt completion , then- Set the
running execution context 's LexicalEnvironment to oldEnv. - If iteratorKind is
async , return ?AsyncIteratorClose (iteratorRecord, status). - If iterationKind is
enumerate , then- Return ? status.
- Else,
Assert : iterationKind isiterate .- Return ?
IteratorClose (iteratorRecord, status).
- Set the
- Let result be
Completion (Evaluation of stmt). - Set the
running execution context 's LexicalEnvironment to oldEnv. - If
LoopContinues (result, labelSet) isfalse , then- If iterationKind is
enumerate , then- Return ?
UpdateEmpty (result, V).
- Return ?
- Else,
Assert : iterationKind isiterate .- Set status to
Completion (UpdateEmpty (result, V)). - If iteratorKind is
async , return ?AsyncIteratorClose (iteratorRecord, status). - Return ?
IteratorClose (iteratorRecord, status).
- If iterationKind is
- If result.[[Value]] is not
empty , set V to result.[[Value]].
- Let nextResult be ?
14.7.5.8 Runtime Semantics: Evaluation
- Let bindingId be the
StringValue ofBindingIdentifier . - Return ?
ResolveBinding (bindingId).
14.7.5.9 EnumerateObjectProperties ( O )
The abstract operation EnumerateObjectProperties takes argument O (an Object) and
returns an
- Return an
iterator object whosenextmethod iterates over all the String-valued keys of enumerable properties of O. Theiterator object is never directly accessible to ECMAScript code. The mechanics and order of enumerating the properties is not specified but must conform to the rules specified below.
The throw and
return methods are next method
processes object properties to determine whether the next method is
ignored. If new properties are added to the target object during enumeration, the newly
added properties are not guaranteed to be processed in the active enumeration. A next method at most once in any enumeration.
Enumerating the properties of the target object includes enumerating properties of its
prototype, and the prototype of the prototype, and so on, recursively; but a property of a
prototype is not processed if it has the same name as a property that has already been
processed by the next method.
The values of [[Enumerable]] attributes are not considered when
determining if a property of a prototype object has already been processed. The enumerable
property names of prototype objects must be obtained by invoking EnumerateObjectProperties
passing the prototype object as the argument. EnumerateObjectProperties must obtain the own
In addition, if neither O nor any object in its prototype chain is a
- the value of the [[Prototype]] internal slot of O or an object in its prototype chain changes,
- a property is removed from O or an object in its prototype chain,
- a property is added to an object in O's prototype chain, or
- the value of the [[Enumerable]] attribute of a property of O or an object in its prototype chain changes.
ECMAScript implementations are not required to implement the algorithm in
The following is an informative definition of an ECMAScript generator function that conforms to these rules:
function* EnumerateObjectProperties(obj) {
const visited = new Set();
for (const key of Reflect.ownKeys(obj)) {
if (typeof key === "symbol") continue;
const desc = Reflect.getOwnPropertyDescriptor(obj, key);
if (desc) {
visited.add(key);
if (desc.enumerable) yield key;
}
}
const proto = Reflect.getPrototypeOf(obj);
if (proto === null) return;
for (const protoKey of EnumerateObjectProperties(proto)) {
if (!visited.has(protoKey)) yield protoKey;
}
}14.7.5.10 For-In Iterator Objects
A For-In
Iterator is an object that represents a specific iteration over some specific
object. For-In Iterator objects are never directly accessible to ECMAScript code; they exist
solely to illustrate the behaviour of
14.7.5.10.1 CreateForInIterator ( object )
The abstract operation CreateForInIterator takes argument object (an Object)
and returns a
- Let iterator be
OrdinaryObjectCreate (%ForInIteratorPrototype% , « [[Object]], [[ObjectWasVisited]], [[VisitedKeys]], [[RemainingKeys]] »). - Set iterator.[[Object]] to object.
- Set iterator.[[ObjectWasVisited]] to
false . - Set iterator.[[VisitedKeys]] to a new empty
List . - Set iterator.[[RemainingKeys]] to a new
empty
List . - Return iterator.
14.7.5.10.2 The %ForInIteratorPrototype% Object
The %ForInIteratorPrototype% object:
- has properties that are inherited by all
For-In Iterator objects . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Iterator.prototype% . - is never directly accessible to ECMAScript code.
- has the following properties:
14.7.5.10.2.1 %ForInIteratorPrototype%.next ( )
- Let O be the
this value. Assert : Ois an Object .Assert : O has all of the internal slots of aFor-In Iterator instance (14.7.5.10.3 ).- Let object be O.[[Object]].
- Repeat,
- If O.[[ObjectWasVisited]] is
false , then- Let keys be ? object.[[OwnPropertyKeys]]().
- For each element key of keys, do
- If key
is a String , then- Append key to O.[[RemainingKeys]].
- If key
- Set O.[[ObjectWasVisited]] to
true .
- Repeat, while O.[[RemainingKeys]] is not empty,
- Let r be the first element of O.[[RemainingKeys]].
- Remove the first element from O.[[RemainingKeys]].
- If O.[[VisitedKeys]]
does not contain r, then
- Let desc be ? object.[[GetOwnProperty]](r).
- If desc is not
undefined , then- Append r to O.[[VisitedKeys]].
- If desc.[[Enumerable]] is
true , returnCreateIteratorResultObject (r,false ).
- Set object to ? object.[[GetPrototypeOf]]().
- Set O.[[Object]] to object.
- Set O.[[ObjectWasVisited]] to
false . - If object is
null , returnCreateIteratorResultObject (undefined ,true ).
- If O.[[ObjectWasVisited]] is
14.7.5.10.3 Properties of For-In Iterator Instances
| Internal Slot | Type | Description |
|---|---|---|
| [[Object]] | an Object | The Object value whose properties are being iterated. |
| [[ObjectWasVisited]] | a Boolean |
|
| [[VisitedKeys]] |
a |
The values that have been emitted by this |
| [[RemainingKeys]] |
a |
The values remaining to be emitted for the current object, before
iterating the properties of its prototype (if its prototype is not
|
14.8 The continue Statement
Syntax
14.8.1 Static Semantics: Early Errors
-
It is a Syntax Error if this
ContinueStatement is not nested, directly or indirectly (but not crossing function orstaticinitialization block boundaries), within anIterationStatement .
14.8.2 Runtime Semantics: Evaluation
- Return
Completion Record { [[Type]]:continue , [[Value]]:empty , [[Target]]:empty }.
- Let label be the
StringValue ofLabelIdentifier . - Return
Completion Record { [[Type]]:continue , [[Value]]:empty , [[Target]]: label }.
14.9 The break Statement
Syntax
14.9.1 Static Semantics: Early Errors
-
It is a Syntax Error if this
BreakStatement is not nested, directly or indirectly (but not crossing function orstaticinitialization block boundaries), within anIterationStatement or aSwitchStatement .
14.9.2 Runtime Semantics: Evaluation
- Return
Completion Record { [[Type]]:break , [[Value]]:empty , [[Target]]:empty }.
- Let label be the
StringValue ofLabelIdentifier . - Return
Completion Record { [[Type]]:break , [[Value]]:empty , [[Target]]: label }.
14.10 The return Statement
Syntax
A return statement causes a function to cease execution and, in most cases,
returns a value to the caller. If return statement may not actually return a value to the caller depending on
surrounding context. For example, in a try block, a return
statement's finally block.
14.10.1 Runtime Semantics: Evaluation
- Return
ReturnCompletion (undefined ).
- Let exprRef be ?
Evaluation ofExpression . - Let exprValue be ?
GetValue (exprRef). - If
GetGeneratorKind () isasync , set exprValue to ?Await (exprValue). - Return
ReturnCompletion (exprValue).
14.11 The with Statement
Use of the with statement is
discouraged in new ECMAScript code. Consider alternatives that are permitted in both
Syntax
The with statement adds an
14.11.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsStrict (this production) istrue . -
It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply the second rule if the extension specified in
14.11.2 Runtime Semantics: Evaluation
- Let val be ?
Evaluation ofExpression . - Let obj be ?
ToObject (?GetValue (val)). - Let oldEnv be the
running execution context 's LexicalEnvironment. - Let newEnv be
NewObjectEnvironment (obj,true , oldEnv). - Set the
running execution context 's LexicalEnvironment to newEnv. - Let C be
Completion (Evaluation ofStatement ). - Set the
running execution context 's LexicalEnvironment to oldEnv. - Return ?
UpdateEmpty (C,undefined ).
No matter how control leaves the embedded
14.12 The switch Statement
Syntax
14.12.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
LexicallyDeclaredNames ofCaseBlock contains any duplicate entries. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofCaseBlock also occurs in theVarDeclaredNames ofCaseBlock .
14.12.2 Runtime Semantics: CaseBlockEvaluation
The
- Return
undefined .
- Let V be
undefined . - Let A be the
List ofCaseClause items inCaseClauses , in source text order. - Let found be
false . - For each
CaseClause C of A, do- If found is
false , then- Set found to ?
CaseClauseIsSelected (C, input).
- Set found to ?
- If found is
true , then- Let R be
Completion (Evaluation of C). - If R.[[Value]] is not
empty , set V to R.[[Value]]. - If R is an
abrupt completion , return ?UpdateEmpty (R, V).
- Let R be
- If found is
- Return V.
- Let V be
undefined . - If the first
CaseClauses is present, then- Let A be the
List ofCaseClause items in the firstCaseClauses , in source text order.
- Let A be the
- Else,
- Let A be a new empty
List .
- Let A be a new empty
- Let found be
false . - For each
CaseClause C of A, do- If found is
false , then- Set found to ?
CaseClauseIsSelected (C, input).
- Set found to ?
- If found is
true , then- Let R be
Completion (Evaluation of C). - If R.[[Value]] is not
empty , set V to R.[[Value]]. - If R is an
abrupt completion , return ?UpdateEmpty (R, V).
- Let R be
- If found is
- Let foundInB be
false . - If the second
CaseClauses is present, then- Let B be the
List ofCaseClause items in the secondCaseClauses , in source text order.
- Let B be the
- Else,
- Let B be a new empty
List .
- Let B be a new empty
- If found is
false , then- For each
CaseClause C of B, do- If foundInB is
false , then- Set foundInB to ?
CaseClauseIsSelected (C, input).
- Set foundInB to ?
- If foundInB is
true , then- Let R be
Completion (Evaluation ofCaseClause C). - If R.[[Value]] is not
empty , set V to R.[[Value]]. - If R is an
abrupt completion , return ?UpdateEmpty (R, V).
- Let R be
- If foundInB is
- For each
- If foundInB is
true , return V. - Let defaultR be
Completion (Evaluation ofDefaultClause ). - If defaultR.[[Value]] is not
empty , set V to defaultR.[[Value]]. - If defaultR is an
abrupt completion , return ?UpdateEmpty (defaultR, V). - NOTE: The following is another complete iteration of the second
CaseClauses . - For each
CaseClause C of B, do- Let R be
Completion (Evaluation ofCaseClause C). - If R.[[Value]] is not
empty , set V to R.[[Value]]. - If R is an
abrupt completion , return ?UpdateEmpty (R, V).
- Let R be
- Return V.
14.12.3 CaseClauseIsSelected ( C, input )
The abstract operation CaseClauseIsSelected takes arguments C (a
Assert : C is an instance of the productionCaseClause : case Expression : StatementList opt - Let exprRef be ?
Evaluation of theExpression of C. - Let clauseSelector be ?
GetValue (exprRef). - Return
IsStrictlyEqual (input, clauseSelector).
This operation does not execute C's
14.12.4 Runtime Semantics: Evaluation
- Let exprRef be ?
Evaluation ofExpression . - Let switchValue be ?
GetValue (exprRef). - Let oldEnv be the
running execution context 's LexicalEnvironment. - Let blockEnv be
NewDeclarativeEnvironment (oldEnv). - Perform
BlockDeclarationInstantiation (CaseBlock , blockEnv). - Set the
running execution context 's LexicalEnvironment to blockEnv. - Let R be
Completion (CaseBlockEvaluation ofCaseBlock with argument switchValue). - Set the
running execution context 's LexicalEnvironment to oldEnv. - Return R.
No matter how control leaves the
- Return
empty .
- Return ?
Evaluation ofStatementList .
- Return
empty .
- Return ?
Evaluation ofStatementList .
14.13 Labelled Statements
Syntax
A break
and continue statements. ECMAScript has no goto statement. A
14.13.1 Static Semantics: Early Errors
- It is a Syntax Error if any source text is matched by this production.
An alternative definition for this rule is provided in
14.13.2 Static Semantics: IsLabelledFunction ( stmt )
The abstract operation IsLabelledFunction takes argument stmt (a
- If stmt is not a
LabelledStatement , returnfalse . - Let item be the
LabelledItem of stmt. - If item is
LabelledItem : FunctionDeclaration true . - Let subStmt be the
Statement of item. - Return
IsLabelledFunction (subStmt).
14.13.3 Runtime Semantics: Evaluation
- Return ?
LabelledEvaluation of thisLabelledStatement with argument « ».
14.13.4 Runtime Semantics: LabelledEvaluation
The
- Let stmtResult be
Completion (LoopEvaluation ofIterationStatement with argument labelSet). - If stmtResult is a
break completion , then- If stmtResult.[[Target]] is
empty , then- If stmtResult.[[Value]] is
empty , set stmtResult toNormalCompletion (undefined ). - Else, set stmtResult to
NormalCompletion (stmtResult.[[Value]]).
- If stmtResult.[[Value]] is
- If stmtResult.[[Target]] is
- Return ? stmtResult.
- Let stmtResult be
Completion (Evaluation ofSwitchStatement ). - If stmtResult is a
break completion , then- If stmtResult.[[Target]] is
empty , then- If stmtResult.[[Value]] is
empty , set stmtResult toNormalCompletion (undefined ). - Else, set stmtResult to
NormalCompletion (stmtResult.[[Value]]).
- If stmtResult.[[Value]] is
- If stmtResult.[[Target]] is
- Return ? stmtResult.
A
- Let label be the
StringValue ofLabelIdentifier . - Let newLabelSet be the
list-concatenation of labelSet and « label ». - Let stmtResult be
Completion (LabelledEvaluation ofLabelledItem with argument newLabelSet). - If stmtResult is a
break completion and stmtResult.[[Target]] is label, then- Set stmtResult to
NormalCompletion (stmtResult.[[Value]]).
- Set stmtResult to
- Return ? stmtResult.
- Return ?
Evaluation ofFunctionDeclaration .
- Return ?
Evaluation ofStatement .
The only two productions of
14.14 The throw Statement
Syntax
14.14.1 Runtime Semantics: Evaluation
- Let exprRef be ?
Evaluation ofExpression . - Let exprValue be ?
GetValue (exprRef). - Return
ThrowCompletion (exprValue).
14.15 The try Statement
Syntax
The try statement encloses a block of code in which an exceptional condition can
occur, such as a runtime error or a throw statement. The catch
clause provides the exception-handling code. When a catch clause catches an exception, its
14.15.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
BoundNames ofCatchParameter contains any duplicate elements. -
It is a Syntax Error if any element of the
BoundNames ofCatchParameter also occurs in theLexicallyDeclaredNames ofBlock . -
It is a Syntax Error if any element of the
BoundNames ofCatchParameter also occurs in theVarDeclaredNames ofBlock .
An alternative
14.15.2 Runtime Semantics: CatchClauseEvaluation
The
- Let oldEnv be the
running execution context 's LexicalEnvironment. - Let catchEnv be
NewDeclarativeEnvironment (oldEnv). - For each element argName of the
BoundNames ofCatchParameter , do- Perform ! catchEnv.CreateMutableBinding(argName,
false ).
- Perform ! catchEnv.CreateMutableBinding(argName,
- Set the
running execution context 's LexicalEnvironment to catchEnv. - Let status be
Completion (BindingInitialization ofCatchParameter with arguments thrownValue and catchEnv). - If status is an
abrupt completion , then- Set the
running execution context 's LexicalEnvironment to oldEnv. - Return ? status.
- Set the
- Let B be
Completion (Evaluation ofBlock ). - Set the
running execution context 's LexicalEnvironment to oldEnv. - Return ? B.
- Return ?
Evaluation ofBlock .
No matter how control leaves the
14.15.3 Runtime Semantics: Evaluation
- Let B be
Completion (Evaluation ofBlock ). - If B is a
throw completion , let C beCompletion (CatchClauseEvaluation ofCatch with argument B.[[Value]]). - Else, let C be B.
- Return ?
UpdateEmpty (C,undefined ).
- Let B be
Completion (Evaluation ofBlock ). - Let F be
Completion (Evaluation ofFinally ). - If F is a
normal completion , set F to B. - Return ?
UpdateEmpty (F,undefined ).
- Let B be
Completion (Evaluation ofBlock ). - If B is a
throw completion , let C beCompletion (CatchClauseEvaluation ofCatch with argument B.[[Value]]). - Else, let C be B.
- Let F be
Completion (Evaluation ofFinally ). - If F is a
normal completion , set F to C. - Return ?
UpdateEmpty (F,undefined ).
14.16 The debugger Statement
Syntax
14.16.1 Runtime Semantics: Evaluation
Evaluating a
- If an
implementation-defined debugging facility is available and enabled, then- Perform an
implementation-defined debugging action. - Return a new
implementation-defined Completion Record .
- Perform an
- Else,
- Return
empty .
- Return
15 ECMAScript Language: Functions and Classes
Various ECMAScript language elements cause the creation of ECMAScript
15.1 Parameter Lists
Syntax
15.1.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
BoundNames ofFormalParameters contains any duplicate elements.
-
It is a Syntax Error if
IsSimpleParameterList ofFormalParameterList isfalse and theBoundNames ofFormalParameterList contains any duplicate elements.
Multiple occurrences of the same
15.1.2 Static Semantics: ContainsExpression
The
- Return
false .
- Return
ContainsExpression ofBindingPropertyList .
- Return
false .
- Return
ContainsExpression ofBindingRestElement .
- Return
ContainsExpression ofBindingElementList .
- Let has be
ContainsExpression ofBindingElementList . - If has is
true , returntrue . - Return
ContainsExpression ofBindingRestElement .
- Let has be
ContainsExpression ofBindingPropertyList . - If has is
true , returntrue . - Return
ContainsExpression ofBindingProperty .
- Let has be
ContainsExpression ofBindingElementList . - If has is
true , returntrue . - Return
ContainsExpression ofBindingElisionElement .
- Return
ContainsExpression ofBindingElement .
- Let has be
IsComputedPropertyKey ofPropertyName . - If has is
true , returntrue . - Return
ContainsExpression ofBindingElement .
- Return
true .
- Return
false .
- Return
true .
- Return
false .
- Return
ContainsExpression ofBindingPattern .
- Return
false .
- If
ContainsExpression ofFormalParameterList istrue , returntrue . - Return
ContainsExpression ofFunctionRestParameter .
- If
ContainsExpression ofFormalParameterList istrue , returntrue . - Return
ContainsExpression ofFormalParameter .
- Return
false .
- Let formals be the
ArrowFormalParameters that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return
ContainsExpression of formals.
- Return
false .
15.1.3 Static Semantics: IsSimpleParameterList
The
- Return
false .
- Return
false .
- Return
true .
- Return
false .
- Return
true .
- Return
false .
- Return
false .
- If
IsSimpleParameterList ofFormalParameterList isfalse , returnfalse . - Return
IsSimpleParameterList ofFormalParameter .
- Return
IsSimpleParameterList ofBindingElement .
- Return
true .
- Let formals be the
ArrowFormalParameters that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return
IsSimpleParameterList of formals.
- Return
true .
- Let head be the
AsyncArrowHead that iscovered byCoverCallExpressionAndAsyncArrowHead . - Return
IsSimpleParameterList of head.
15.1.4 Static Semantics: HasInitializer
The
- Return
false .
- Return
true .
- Return
false .
- Return
true .
- If
HasInitializer ofFormalParameterList istrue , returntrue . - Return
HasInitializer ofFormalParameter .
15.1.5 Static Semantics: ExpectedArgumentCount
The
- Return 0.
- Return the
ExpectedArgumentCount ofFormalParameterList .
The ExpectedArgumentCount of a
- If
HasInitializer ofFormalParameter istrue , return 0. - Return 1.
- Let count be the
ExpectedArgumentCount ofFormalParameterList . - If
HasInitializer ofFormalParameterList istrue orHasInitializer ofFormalParameter istrue , return count. - Return count + 1.
- Return 1.
- Let formals be the
ArrowFormalParameters that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return the
ExpectedArgumentCount of formals.
- If
HasInitializer ofFormalParameter istrue , return 0. - Return 1.
- Return 1.
15.2 Function Definitions
Syntax
15.2.1 Static Semantics: Early Errors
-
If
IsStrict (FormalParameters ) istrue , the Early Error rules forUniqueFormalParameters : FormalParameters -
If
BindingIdentifier is present andIsStrict (BindingIdentifier ) istrue , it is a Syntax Error if theStringValue ofBindingIdentifier is either"eval" or"arguments" . -
It is a Syntax Error if
FunctionBodyContainsUseStrict ofFunctionBody istrue andIsSimpleParameterList ofFormalParameters isfalse . -
It is a Syntax Error if any element of the
BoundNames ofFormalParameters also occurs in theLexicallyDeclaredNames ofFunctionBody . -
It is a Syntax Error if
FormalParameters Contains SuperProperty istrue . -
It is a Syntax Error if
FunctionBody Contains SuperProperty istrue . -
It is a Syntax Error if
FormalParameters Contains SuperCall istrue . -
It is a Syntax Error if
FunctionBody Contains SuperCall istrue .
The
-
It is a Syntax Error if the
LexicallyDeclaredNames ofFunctionStatementList contains any duplicate entries. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofFunctionStatementList also occurs in theVarDeclaredNames ofFunctionStatementList . -
It is a Syntax Error if
ContainsDuplicateLabels ofFunctionStatementList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedBreakTarget ofFunctionStatementList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedContinueTarget ofFunctionStatementList with arguments « » and « » istrue .
15.2.2 Static Semantics: FunctionBodyContainsUseStrict
The
- If the
Directive Prologue ofFunctionBody contains aUse Strict Directive , returntrue ; otherwise returnfalse .
15.2.3 Runtime Semantics: EvaluateFunctionBody
The
- Perform ?
FunctionDeclarationInstantiation (functionObject, argumentsList). - Perform ?
Evaluation ofFunctionStatementList . - NOTE: If the previous step resulted in a
normal completion , then evaluation finished by proceeding past the end of theFunctionStatementList . - Return
ReturnCompletion (undefined ).
15.2.4 Runtime Semantics: InstantiateOrdinaryFunctionObject
The
- Let name be the
StringValue ofBindingIdentifier . - Let sourceText be the
source text matched by FunctionDeclaration . - Let F be
OrdinaryFunctionCreate (%Function.prototype% , sourceText,FormalParameters ,FunctionBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F, name). - Perform
MakeConstructor (F). - Return F.
- Let sourceText be the
source text matched by FunctionDeclaration . - Let F be
OrdinaryFunctionCreate (%Function.prototype% , sourceText,FormalParameters ,FunctionBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F,"default" ). - Perform
MakeConstructor (F). - Return F.
An anonymous export default declaration, and its function code is
therefore always
15.2.5 Runtime Semantics: InstantiateOrdinaryFunctionExpression
The
- If name is not present, set name to
"" . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by FunctionExpression . - Let closure be
OrdinaryFunctionCreate (%Function.prototype% , sourceText,FormalParameters ,FunctionBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (closure, name). - Perform
MakeConstructor (closure). - Return closure.
Assert : name is not present.- Set name to the
StringValue ofBindingIdentifier . - Let outerEnv be the
running execution context 's LexicalEnvironment. - Let funcEnv be
NewDeclarativeEnvironment (outerEnv). - Perform ! funcEnv.CreateImmutableBinding(name,
false ). - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by FunctionExpression . - Let closure be
OrdinaryFunctionCreate (%Function.prototype% , sourceText,FormalParameters ,FunctionBody ,non-lexical-this , funcEnv, privateEnv). - Perform
SetFunctionName (closure, name). - Perform
MakeConstructor (closure). - Perform ! funcEnv.InitializeBinding(name, closure).
- Return closure.
The
15.2.6 Runtime Semantics: Evaluation
- Return
empty .
An alternative semantics is provided in
- Return
empty .
A
- Return
undefined .
15.3 Arrow Function Definitions
Syntax
Supplemental Syntax
When processing an instance of the production
the interpretation of
15.3.1 Static Semantics: Early Errors
-
It is a Syntax Error if
ArrowParameters Contains YieldExpression istrue . -
It is a Syntax Error if
ArrowParameters Contains AwaitExpression istrue . -
It is a Syntax Error if
ConciseBodyContainsUseStrict ofConciseBody istrue andIsSimpleParameterList ofArrowParameters isfalse . -
It is a Syntax Error if any element of the
BoundNames ofArrowParameters also occurs in theLexicallyDeclaredNames ofConciseBody .
15.3.2 Static Semantics: ConciseBodyContainsUseStrict
The
- Return
false .
- Return
FunctionBodyContainsUseStrict ofFunctionBody .
15.3.3 Runtime Semantics: EvaluateConciseBody
The
- Perform ?
FunctionDeclarationInstantiation (functionObject, argumentsList). - Return ?
Evaluation ofExpressionBody .
15.3.4 Runtime Semantics: InstantiateArrowFunctionExpression
The
- If name is not present, set name to
"" . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by ArrowFunction . - Let closure be
OrdinaryFunctionCreate (%Function.prototype% , sourceText,ArrowParameters ,ConciseBody ,lexical-this , env, privateEnv). - Perform
SetFunctionName (closure, name). - Return closure.
An arguments, super,
this, or new.target. Any reference to arguments,
super, this, or new.target within an super, the super is always contained within a non-super is accessible via the env that is captured by
the
15.3.5 Runtime Semantics: Evaluation
- Return
InstantiateArrowFunctionExpression ofArrowFunction .
- Let exprRef be ?
Evaluation ofAssignmentExpression . - Let exprValue be ?
GetValue (exprRef). - Return
ReturnCompletion (exprValue).
15.4 Method Definitions
Syntax
15.4.1 Static Semantics: Early Errors
-
It is a Syntax Error if
FunctionBodyContainsUseStrict ofFunctionBody istrue andIsSimpleParameterList ofUniqueFormalParameters isfalse . -
It is a Syntax Error if any element of the
BoundNames ofUniqueFormalParameters also occurs in theLexicallyDeclaredNames ofFunctionBody .
-
It is a Syntax Error if the
BoundNames ofPropertySetParameterList contains any duplicate elements. -
It is a Syntax Error if
FunctionBodyContainsUseStrict ofFunctionBody istrue andIsSimpleParameterList ofPropertySetParameterList isfalse . -
It is a Syntax Error if any element of the
BoundNames ofPropertySetParameterList also occurs in theLexicallyDeclaredNames ofFunctionBody .
15.4.2 Static Semantics: HasDirectSuper
The
- If
UniqueFormalParameters Contains SuperCall istrue , returntrue . - Return
FunctionBody Contains SuperCall .
- Return
FunctionBody Contains SuperCall .
- If
PropertySetParameterList Contains SuperCall istrue , returntrue . - Return
FunctionBody Contains SuperCall .
- If
UniqueFormalParameters Contains SuperCall istrue , returntrue . - Return
GeneratorBody Contains SuperCall .
- If
UniqueFormalParameters Contains SuperCall istrue , returntrue . - Return
AsyncGeneratorBody Contains SuperCall .
- If
UniqueFormalParameters Contains SuperCall istrue , returntrue . - Return
AsyncFunctionBody Contains SuperCall .
15.4.3 Static Semantics: SpecialMethod
The
- Return
false .
- Return
true .
15.4.4 Runtime Semantics: DefineMethod
The
- Let propKey be ?
Evaluation ofClassElementName . - Let env be the
running execution context 's LexicalEnvironment. - Let privateEnv be the
running execution context 's PrivateEnvironment. - If functionPrototype is present, then
- Let prototype be functionPrototype.
- Else,
- Let prototype be
%Function.prototype% .
- Let prototype be
- Let sourceText be the
source text matched by MethodDefinition . - Let closure be
OrdinaryFunctionCreate (prototype, sourceText,UniqueFormalParameters ,FunctionBody ,non-lexical-this , env, privateEnv). - Perform
MakeMethod (closure, object). - Return the
Record { [[Key]]: propKey, [[Closure]]: closure }.
15.4.5 Runtime Semantics: MethodDefinitionEvaluation
The
- Let methodDef be ?
DefineMethod ofMethodDefinition with argument object. - Perform
SetFunctionName (methodDef.[[Closure]], methodDef.[[Key]]). - Return ?
DefineMethodProperty (object, methodDef.[[Key]], methodDef.[[Closure]], enumerable).
- Let propKey be ?
Evaluation ofClassElementName . - Let env be the
running execution context 's LexicalEnvironment. - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by MethodDefinition . - Let formalParameterList be an instance of the production
FormalParameters : [empty] - Let closure be
OrdinaryFunctionCreate (%Function.prototype% , sourceText, formalParameterList,FunctionBody ,non-lexical-this , env, privateEnv). - Perform
MakeMethod (closure, object). - Perform
SetFunctionName (closure, propKey,"get" ). - If propKey is a
Private Name , then- Return
PrivateElement { [[Key]]: propKey, [[Kind]]:accessor , [[Get]]: closure, [[Set]]:undefined }.
- Return
- Else,
- Let desc be the PropertyDescriptor { [[Get]]: closure, [[Enumerable]]: enumerable, [[Configurable]]:
true }. - Perform ?
DefinePropertyOrThrow (object, propKey, desc). - Return
unused .
- Let desc be the PropertyDescriptor { [[Get]]: closure, [[Enumerable]]: enumerable, [[Configurable]]:
- Let propKey be ?
Evaluation ofClassElementName . - Let env be the
running execution context 's LexicalEnvironment. - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by MethodDefinition . - Let closure be
OrdinaryFunctionCreate (%Function.prototype% , sourceText,PropertySetParameterList ,FunctionBody ,non-lexical-this , env, privateEnv). - Perform
MakeMethod (closure, object). - Perform
SetFunctionName (closure, propKey,"set" ). - If propKey is a
Private Name , then- Return
PrivateElement { [[Key]]: propKey, [[Kind]]:accessor , [[Get]]:undefined , [[Set]]: closure }.
- Return
- Else,
- Let desc be the PropertyDescriptor { [[Set]]: closure, [[Enumerable]]: enumerable, [[Configurable]]:
true }. - Perform ?
DefinePropertyOrThrow (object, propKey, desc). - Return
unused .
- Let desc be the PropertyDescriptor { [[Set]]: closure, [[Enumerable]]: enumerable, [[Configurable]]:
- Let propKey be ?
Evaluation ofClassElementName . - Let env be the
running execution context 's LexicalEnvironment. - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by GeneratorMethod . - Let closure be
OrdinaryFunctionCreate (%GeneratorFunction.prototype% , sourceText,UniqueFormalParameters ,GeneratorBody ,non-lexical-this , env, privateEnv). - Perform
MakeMethod (closure, object). - Perform
SetFunctionName (closure, propKey). - Let prototype be
OrdinaryObjectCreate (%GeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return ?
DefineMethodProperty (object, propKey, closure, enumerable).
- Let propKey be ?
Evaluation ofClassElementName . - Let env be the
running execution context 's LexicalEnvironment. - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncGeneratorMethod . - Let closure be
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% , sourceText,UniqueFormalParameters ,AsyncGeneratorBody ,non-lexical-this , env, privateEnv). - Perform
MakeMethod (closure, object). - Perform
SetFunctionName (closure, propKey). - Let prototype be
OrdinaryObjectCreate (%AsyncGeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return ?
DefineMethodProperty (object, propKey, closure, enumerable).
- Let propKey be ?
Evaluation ofClassElementName . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncMethod . - Let closure be
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText,UniqueFormalParameters ,AsyncFunctionBody ,non-lexical-this , env, privateEnv). - Perform
MakeMethod (closure, object). - Perform
SetFunctionName (closure, propKey). - Return ?
DefineMethodProperty (object, propKey, closure, enumerable).
15.5 Generator Function Definitions
Syntax
The syntactic context immediately following yield requires use of the
15.5.1 Static Semantics: Early Errors
-
It is a Syntax Error if
HasDirectSuper ofGeneratorMethod istrue . -
It is a Syntax Error if
UniqueFormalParameters Contains YieldExpression istrue . -
It is a Syntax Error if
FunctionBodyContainsUseStrict ofGeneratorBody istrue andIsSimpleParameterList ofUniqueFormalParameters isfalse . -
It is a Syntax Error if any element of the
BoundNames ofUniqueFormalParameters also occurs in theLexicallyDeclaredNames ofGeneratorBody .
-
If
IsStrict (FormalParameters ) istrue , the Early Error rules forUniqueFormalParameters : FormalParameters -
If
BindingIdentifier is present andIsStrict (BindingIdentifier ) istrue , it is a Syntax Error if theStringValue ofBindingIdentifier is either"eval" or"arguments" . -
It is a Syntax Error if
FunctionBodyContainsUseStrict ofGeneratorBody istrue andIsSimpleParameterList ofFormalParameters isfalse . -
It is a Syntax Error if any element of the
BoundNames ofFormalParameters also occurs in theLexicallyDeclaredNames ofGeneratorBody . -
It is a Syntax Error if
FormalParameters Contains YieldExpression istrue . -
It is a Syntax Error if
FormalParameters Contains SuperProperty istrue . -
It is a Syntax Error if
GeneratorBody Contains SuperProperty istrue . -
It is a Syntax Error if
FormalParameters Contains SuperCall istrue . -
It is a Syntax Error if
GeneratorBody Contains SuperCall istrue .
15.5.2 Runtime Semantics: EvaluateGeneratorBody
The
- Perform ?
FunctionDeclarationInstantiation (functionObject, argumentsList). - Let G be ?
OrdinaryCreateFromConstructor (functionObject,"%GeneratorPrototype%" , « [[GeneratorState]], [[GeneratorContext]], [[GeneratorBrand]] »). - Set G.[[GeneratorBrand]] to
empty . - Set G.[[GeneratorState]] to
suspended-start . - Perform
GeneratorStart (G,FunctionBody ). - Return
ReturnCompletion (G).
15.5.3 Runtime Semantics: InstantiateGeneratorFunctionObject
The
- Let name be the
StringValue ofBindingIdentifier . - Let sourceText be the
source text matched by GeneratorDeclaration . - Let F be
OrdinaryFunctionCreate (%GeneratorFunction.prototype% , sourceText,FormalParameters ,GeneratorBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F, name). - Let prototype be
OrdinaryObjectCreate (%GeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return F.
- Let sourceText be the
source text matched by GeneratorDeclaration . - Let F be
OrdinaryFunctionCreate (%GeneratorFunction.prototype% , sourceText,FormalParameters ,GeneratorBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F,"default" ). - Let prototype be
OrdinaryObjectCreate (%GeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return F.
An anonymous export default declaration, and its function code is
therefore always
15.5.4 Runtime Semantics: InstantiateGeneratorFunctionExpression
The
- If name is not present, set name to
"" . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by GeneratorExpression . - Let closure be
OrdinaryFunctionCreate (%GeneratorFunction.prototype% , sourceText,FormalParameters ,GeneratorBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (closure, name). - Let prototype be
OrdinaryObjectCreate (%GeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return closure.
Assert : name is not present.- Set name to the
StringValue ofBindingIdentifier . - Let outerEnv be the
running execution context 's LexicalEnvironment. - Let funcEnv be
NewDeclarativeEnvironment (outerEnv). - Perform ! funcEnv.CreateImmutableBinding(name,
false ). - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by GeneratorExpression . - Let closure be
OrdinaryFunctionCreate (%GeneratorFunction.prototype% , sourceText,FormalParameters ,GeneratorBody ,non-lexical-this , funcEnv, privateEnv). - Perform
SetFunctionName (closure, name). - Let prototype be
OrdinaryObjectCreate (%GeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Perform ! funcEnv.InitializeBinding(name, closure).
- Return closure.
The
15.5.5 Runtime Semantics: Evaluation
- Return ?
Yield (undefined ).
- Let exprRef be ?
Evaluation ofAssignmentExpression . - Let value be ?
GetValue (exprRef). - Return ?
Yield (value).
- Let generatorKind be
GetGeneratorKind (). Assert : generatorKind is eithersync orasync .- Let exprRef be ?
Evaluation ofAssignmentExpression . - Let value be ?
GetValue (exprRef). - Let iteratorRecord be ?
GetIterator (value, generatorKind). - Let iterator be iteratorRecord.[[Iterator]].
- Let received be
NormalCompletion (undefined ). - Repeat,
- If received is a
normal completion , then- Let innerResult be ?
Call (iteratorRecord.[[NextMethod]], iteratorRecord.[[Iterator]], « received.[[Value]] »). - If generatorKind is
async , set innerResult to ?Await (innerResult). - If innerResult
is not an Object , throw aTypeError exception. - Let done be ?
IteratorComplete (innerResult). - If done is
true , then- Return ?
IteratorValue (innerResult).
- Return ?
- If generatorKind is
async , set received toCompletion (AsyncGeneratorYield (?IteratorValue (innerResult))). - Else, set received to
Completion (GeneratorYield (innerResult)).
- Let innerResult be ?
- Else if received is a
throw completion , then- Let throw be ?
GetMethod (iterator,"throw" ). - If throw is not
undefined , then- Let innerResult be ?
Call (throw, iterator, « received.[[Value]] »). - If generatorKind is
async , set innerResult to ?Await (innerResult). - NOTE: Exceptions from the inner
iterator throwmethod are propagated.Normal completions from an innerthrowmethod are processed similarly to an innernext. - If innerResult
is not an Object , throw aTypeError exception. - Let done be ?
IteratorComplete (innerResult). - If done is
true , then- Return ?
IteratorValue (innerResult).
- Return ?
- If generatorKind is
async , set received toCompletion (AsyncGeneratorYield (?IteratorValue (innerResult))). - Else, set received to
Completion (GeneratorYield (innerResult)).
- Let innerResult be ?
- Else,
- NOTE: If iterator does not have a
throwmethod, this throw is going to terminate theyield*loop. But first we need to give iterator a chance to clean up. - Let closeCompletion be
NormalCompletion (empty ). - If generatorKind is
async , perform ?AsyncIteratorClose (iteratorRecord, closeCompletion). - Else, perform ?
IteratorClose (iteratorRecord, closeCompletion). - NOTE: The next step throws a
TypeError to indicate that there was ayield*protocol violation: iterator does not have athrowmethod. - Throw a
TypeError exception.
- NOTE: If iterator does not have a
- Let throw be ?
- Else,
Assert : received is areturn completion .- Let return be ?
GetMethod (iterator,"return" ). - If return is
undefined , then- Set value to received.[[Value]].
- If generatorKind is
async , then- Set value to ?
Await (value).
- Set value to ?
- Return
ReturnCompletion (value).
- Let innerReturnResult be ?
Call (return, iterator, « received.[[Value]] »). - If generatorKind is
async , set innerReturnResult to ?Await (innerReturnResult). - If innerReturnResult
is not an Object , throw aTypeError exception. - Let done be ?
IteratorComplete (innerReturnResult). - If done is
true , then- Set value to ?
IteratorValue (innerReturnResult). - Return
ReturnCompletion (value).
- Set value to ?
- If generatorKind is
async , set received toCompletion (AsyncGeneratorYield (?IteratorValue (innerReturnResult))). - Else, set received to
Completion (GeneratorYield (innerReturnResult)).
- If received is a
15.6 Async Generator Function Definitions
Syntax
15.6.1 Static Semantics: Early Errors
- It is a Syntax Error if
HasDirectSuper ofAsyncGeneratorMethod istrue . - It is a Syntax Error if
UniqueFormalParameters Contains YieldExpression istrue . - It is a Syntax Error if
UniqueFormalParameters Contains AwaitExpression istrue . - It is a Syntax Error if
FunctionBodyContainsUseStrict ofAsyncGeneratorBody istrue andIsSimpleParameterList ofUniqueFormalParameters isfalse . - It is a Syntax Error if any element of the
BoundNames ofUniqueFormalParameters also occurs in theLexicallyDeclaredNames ofAsyncGeneratorBody .
- If
IsStrict (FormalParameters ) istrue , the Early Error rules forUniqueFormalParameters : FormalParameters - If
BindingIdentifier is present andIsStrict (BindingIdentifier ) istrue , it is a Syntax Error if theStringValue ofBindingIdentifier is either"eval" or"arguments" . - It is a Syntax Error if
FunctionBodyContainsUseStrict ofAsyncGeneratorBody istrue andIsSimpleParameterList ofFormalParameters isfalse . - It is a Syntax Error if any element of the
BoundNames ofFormalParameters also occurs in theLexicallyDeclaredNames ofAsyncGeneratorBody . - It is a Syntax Error if
FormalParameters Contains YieldExpression istrue . - It is a Syntax Error if
FormalParameters Contains AwaitExpression istrue . - It is a Syntax Error if
FormalParameters Contains SuperProperty istrue . - It is a Syntax Error if
AsyncGeneratorBody Contains SuperProperty istrue . - It is a Syntax Error if
FormalParameters Contains SuperCall istrue . - It is a Syntax Error if
AsyncGeneratorBody Contains SuperCall istrue .
15.6.2 Runtime Semantics: EvaluateAsyncGeneratorBody
The
- Perform ?
FunctionDeclarationInstantiation (functionObject, argumentsList). - Let generator be ?
OrdinaryCreateFromConstructor (functionObject,"%AsyncGeneratorPrototype%" , « [[AsyncGeneratorState]], [[AsyncGeneratorContext]], [[AsyncGeneratorQueue]], [[GeneratorBrand]] »). - Set generator.[[GeneratorBrand]] to
empty . - Set generator.[[AsyncGeneratorState]] to
suspended-start . - Perform
AsyncGeneratorStart (generator,FunctionBody ). - Return
ReturnCompletion (generator).
15.6.3 Runtime Semantics: InstantiateAsyncGeneratorFunctionObject
The
- Let name be the
StringValue ofBindingIdentifier . - Let sourceText be the
source text matched by AsyncGeneratorDeclaration . - Let F be
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% , sourceText,FormalParameters ,AsyncGeneratorBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F, name). - Let prototype be
OrdinaryObjectCreate (%AsyncGeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return F.
- Let sourceText be the
source text matched by AsyncGeneratorDeclaration . - Let F be
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% , sourceText,FormalParameters ,AsyncGeneratorBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F,"default" ). - Let prototype be
OrdinaryObjectCreate (%AsyncGeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return F.
An anonymous export default declaration.
15.6.4 Runtime Semantics: InstantiateAsyncGeneratorFunctionExpression
The
- If name is not present, set name to
"" . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncGeneratorExpression . - Let closure be
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% , sourceText,FormalParameters ,AsyncGeneratorBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (closure, name). - Let prototype be
OrdinaryObjectCreate (%AsyncGeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return closure.
Assert : name is not present.- Set name to the
StringValue ofBindingIdentifier . - Let outerEnv be the
running execution context 's LexicalEnvironment. - Let funcEnv be
NewDeclarativeEnvironment (outerEnv). - Perform ! funcEnv.CreateImmutableBinding(name,
false ). - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncGeneratorExpression . - Let closure be
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% , sourceText,FormalParameters ,AsyncGeneratorBody ,non-lexical-this , funcEnv, privateEnv). - Perform
SetFunctionName (closure, name). - Let prototype be
OrdinaryObjectCreate (%AsyncGeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Perform ! funcEnv.InitializeBinding(name, closure).
- Return closure.
The
15.6.5 Runtime Semantics: Evaluation
15.7 Class Definitions
Syntax
A class definition is always
15.7.1 Static Semantics: Early Errors
-
It is a Syntax Error if
ClassHeritage is not present and the following algorithm returnstrue :- Let constructor be the
ConstructorMethod ofClassBody . - If constructor is
empty , returnfalse . - Return
HasDirectSuper of constructor.
- Let constructor be the
-
It is a Syntax Error if the
PrototypePropertyNameList ofClassElementList contains more than one occurrence of"constructor" . -
It is a Syntax Error if the
PrivateBoundIdentifiers ofClassElementList contains any duplicate entries, unless the name is used once for a getter and once for a setter and in no other entries, and the getter and setter are either both static or both non-static.
-
It is a Syntax Error if the
PropName ofMethodDefinition is not"constructor" andHasDirectSuper ofMethodDefinition istrue . -
It is a Syntax Error if the
PropName ofMethodDefinition is"constructor" andSpecialMethod ofMethodDefinition istrue .
-
It is a Syntax Error if
HasDirectSuper ofMethodDefinition istrue . -
It is a Syntax Error if the
PropName ofMethodDefinition is"prototype" .
- It is a Syntax Error if the
PropName ofFieldDefinition is"constructor" .
-
It is a Syntax Error if the
PropName ofFieldDefinition is either"prototype" or"constructor" .
- It is a Syntax Error if
Initializer is present andContainsArguments ofInitializer istrue . - It is a Syntax Error if
Initializer is present andInitializer Contains SuperCall istrue .
- It is a Syntax Error if the
StringValue ofPrivateIdentifier is"#constructor" .
-
It is a Syntax Error if the
LexicallyDeclaredNames ofClassStaticBlockStatementList contains any duplicate entries. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofClassStaticBlockStatementList also occurs in theVarDeclaredNames ofClassStaticBlockStatementList . -
It is a Syntax Error if
ContainsDuplicateLabels ofClassStaticBlockStatementList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedBreakTarget ofClassStaticBlockStatementList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedContinueTarget ofClassStaticBlockStatementList with arguments « » and « » istrue . -
It is a Syntax Error if
ContainsArguments ofClassStaticBlockStatementList istrue . -
It is a Syntax Error if
ClassStaticBlockStatementList Contains SuperCall istrue . -
It is a Syntax Error if
ClassStaticBlockStatementList Contains awaitistrue .
15.7.2 Static Semantics: ClassElementKind
The
- If the
PropName ofMethodDefinition is"constructor" , returnconstructor-method . - Return
non-constructor-method .
- Return
non-constructor-method .
- Return
non-constructor-method .
- Return
empty .
15.7.3 Static Semantics: ConstructorMethod
The
- If the
ClassElementKind ofClassElement isconstructor-method , returnClassElement . - Return
empty .
- Let head be the
ConstructorMethod ofClassElementList . - If head is not
empty , return head. - If the
ClassElementKind ofClassElement isconstructor-method , returnClassElement . - Return
empty .
Early Error rules ensure that there is only one method definition named
15.7.4 Static Semantics: IsStatic
The
- Return
false .
- Return
true .
- Return
false .
- Return
true .
- Return
true .
- Return
false .
15.7.5 Static Semantics: NonConstructorElements
The
- If the
ClassElementKind ofClassElement isnon-constructor-method , then- Return «
ClassElement ».
- Return «
- Return a new empty
List .
- Let list be the
NonConstructorElements ofClassElementList . - If the
ClassElementKind ofClassElement isnon-constructor-method , then- Append
ClassElement to the end of list.
- Append
- Return list.
15.7.6 Static Semantics: PrototypePropertyNameList
The
- Let propName be the
PropName ofClassElement . - If propName is
empty , return a new emptyList . - If
IsStatic ofClassElement istrue , return a new emptyList . - Return « propName ».
- Let list be the
PrototypePropertyNameList ofClassElementList . - Let propName be the
PropName ofClassElement . - If propName is
empty , return list. - If
IsStatic ofClassElement istrue , return list. - Return the
list-concatenation of list and « propName ».
15.7.7 Static Semantics: AllPrivateIdentifiersValid
The
Every grammar production alternative in this specification which is not listed below implicitly has the following default definition of AllPrivateIdentifiersValid:
- For each child node child of this
Parse Node , do- If child is an instance of a nonterminal, then
- If
AllPrivateIdentifiersValid of child with argument names isfalse , returnfalse .
- If
- If child is an instance of a nonterminal, then
- Return
true .
- If names contains the
StringValue ofPrivateIdentifier , then- Return
AllPrivateIdentifiersValid ofMemberExpression with argument names.
- Return
- Return
false .
- If names contains the
StringValue ofPrivateIdentifier , then- Return
AllPrivateIdentifiersValid ofCallExpression with argument names.
- Return
- Return
false .
- If names contains the
StringValue ofPrivateIdentifier , returntrue . - Return
false .
- If names contains the
StringValue ofPrivateIdentifier , then- Return
AllPrivateIdentifiersValid ofOptionalChain with argument names.
- Return
- Return
false .
- Let newNames be the
list-concatenation of names and thePrivateBoundIdentifiers ofClassBody . - Return
AllPrivateIdentifiersValid ofClassElementList with argument newNames.
- If names contains the
StringValue ofPrivateIdentifier , then- Return
AllPrivateIdentifiersValid ofShiftExpression with argument names.
- Return
- Return
false .
15.7.8 Static Semantics: PrivateBoundIdentifiers
The
- Return the
PrivateBoundIdentifiers ofClassElementName .
- Return a
List whose sole element is theStringValue ofPrivateIdentifier .
- Return a new empty
List .
- Let names1 be the
PrivateBoundIdentifiers ofClassElementList . - Let names2 be the
PrivateBoundIdentifiers ofClassElement . - Return the
list-concatenation of names1 and names2.
- Return the
PrivateBoundIdentifiers ofClassElementName .
15.7.9 Static Semantics: ContainsArguments
The
Every grammar production alternative in this specification which is not listed below implicitly has the following default definition of ContainsArguments:
- For each child node child of this
Parse Node , do- If child is an instance of a nonterminal, then
- If
ContainsArguments of child istrue , returntrue .
- If
- If child is an instance of a nonterminal, then
- Return
false .
- If the
StringValue ofIdentifier is"arguments" , returntrue . - Return
false .
- Return
false .
- Return
ContainsArguments ofClassElementName .
15.7.10 Runtime Semantics: ClassFieldDefinitionEvaluation
The
- Let name be ?
Evaluation ofClassElementName . - If
Initializer is present, then- Let formalParameterList be an instance of the production
FormalParameters : [empty] - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the empty sequence of Unicode code points.
- Let initializer be
OrdinaryFunctionCreate (%Function.prototype% , sourceText, formalParameterList,Initializer ,non-lexical-this , env, privateEnv). - Perform
MakeMethod (initializer, homeObject). - Set initializer.[[ClassFieldInitializerName]] to name.
- Let formalParameterList be an instance of the production
- Else,
- Let initializer be
empty .
- Let initializer be
- Return the
ClassFieldDefinition Record { [[Name]]: name, [[Initializer]]: initializer }.
15.7.11 Runtime Semantics: ClassStaticBlockDefinitionEvaluation
The
- Let lex be the
running execution context 's LexicalEnvironment. - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the empty sequence of Unicode code points.
- Let formalParameters be an instance of the production
FormalParameters : [empty] - Let bodyFunction be
OrdinaryFunctionCreate (%Function.prototype% , sourceText, formalParameters,ClassStaticBlockBody ,non-lexical-this , lex, privateEnv). - Perform
MakeMethod (bodyFunction, homeObject). - Return the
ClassStaticBlockDefinition Record { [[BodyFunction]]: bodyFunction }.
15.7.12 Runtime Semantics: EvaluateClassStaticBlockBody
The
Assert : functionObject is a synthetic function created byClassStaticBlockDefinitionEvaluation step5 .- Perform !
FunctionDeclarationInstantiation (functionObject, « »). - Perform ?
Evaluation ofClassStaticBlockStatementList . - Return
ReturnCompletion (undefined ).
15.7.13 Runtime Semantics: ClassElementEvaluation
The
- Return ?
ClassFieldDefinitionEvaluation ofFieldDefinition with argument object.
- Return ?
MethodDefinitionEvaluation ofMethodDefinition with arguments object andfalse .
- Return the
ClassStaticBlockDefinitionEvaluation ofClassStaticBlock with argument object.
- Return
unused .
15.7.14 Runtime Semantics: ClassDefinitionEvaluation
The
For ease of specification, private methods and accessors are included alongside private fields in the [[PrivateElements]] slot of class instances. However, any given object has either all or none of the private methods and accessors defined by a given class. This feature has been designed so that implementations may choose to implement private methods and accessors using a strategy which does not require tracking each method or accessor individually.
For example, an implementation could directly associate instance private methods with
their corresponding this value. Looking up an instance private method on an object then
consists of checking that the class
This differs from private fields: because field initializers can throw during class instantiation, an individual object may have some proper subset of the private fields of a given class, and so private fields must in general be tracked individually.
It is defined piecewise over the following productions:
- Let env be the LexicalEnvironment of the
running execution context . - Let classEnv be
NewDeclarativeEnvironment (env). - If classBinding is not
undefined , then- Perform
! classEnv.CreateImmutableBinding(classBinding,
true ).
- Perform
! classEnv.CreateImmutableBinding(classBinding,
- Let outerPrivateEnvironment be the
running execution context 's PrivateEnvironment. - Let classPrivateEnvironment be
NewPrivateEnvironment (outerPrivateEnvironment). - If
ClassBody is present, then- For each String dn of the
PrivateBoundIdentifiers ofClassBody , do- If classPrivateEnvironment.[[Names]]
contains a
Private Name pn such that pn.[[Description]] is dn, thenAssert : This is only possible for getter/setter pairs.
- Else,
- Let name be a new
Private Name whose [[Description]] is dn. - Append name to classPrivateEnvironment.[[Names]].
- Let name be a new
- If classPrivateEnvironment.[[Names]]
contains a
- For each String dn of the
- If
ClassHeritage is not present, then- Let protoParent be
%Object.prototype% . - Let constructorParent be
%Function.prototype% .
- Let protoParent be
- Else,
- Set the
running execution context 's LexicalEnvironment to classEnv. - NOTE: The
running execution context 's PrivateEnvironment is outerPrivateEnvironment when evaluatingClassHeritage . - Let superclassRef be
Completion (Evaluation ofClassHeritage ). - Set the
running execution context 's LexicalEnvironment to env. - Let superclass be ?
GetValue (? superclassRef). - If superclass is
null , then- Let protoParent be
null . - Let constructorParent be
%Function.prototype% .
- Let protoParent be
- Else if
IsConstructor (superclass) isfalse , then- Throw a
TypeError exception.
- Throw a
- Else,
- Let protoParent be ?
Get (superclass,"prototype" ). - If protoParent
is not an Object and protoParent is notnull , throw aTypeError exception. - Let constructorParent be superclass.
- Let protoParent be ?
- Set the
- Let proto be
OrdinaryObjectCreate (protoParent). - If
ClassBody is not present, let constructor beempty . - Else, let constructor be the
ConstructorMethod ofClassBody . - Set the
running execution context 's LexicalEnvironment to classEnv. - Set the
running execution context 's PrivateEnvironment to classPrivateEnvironment. - If constructor is
empty , then- Let defaultConstructor be a new
Abstract Closure with no parameters that captures nothing and performs the following steps when called:- Let args be the
List of arguments that was passed to this function by [[Call]] or [[Construct]]. - If NewTarget is
undefined , throw aTypeError exception. - Let F be the
active function object . - If F.[[ConstructorKind]] is
derived , then- NOTE: This branch behaves similarly to
constructor(...args) { super(...args); }. The most notable distinction is that while the aforementionedECMAScript source text observably calls the%Symbol.iterator% method on%Array.prototype%, this function does not. - Let func be ! F.[[GetPrototypeOf]]().
- If
IsConstructor (func) isfalse , throw aTypeError exception. - Let result be ?
Construct (func, args, NewTarget).
- NOTE: This branch behaves similarly to
- Else,
- NOTE: This branch behaves similarly to
constructor() {}. - Let result be ?
OrdinaryCreateFromConstructor (NewTarget,"%Object.prototype%" ).
- NOTE: This branch behaves similarly to
- Perform ?
InitializeInstanceElements (result, F). - Return
NormalCompletion (result).
- Let args be the
- Let F be
CreateBuiltinFunction (defaultConstructor, 0, className, « [[ConstructorKind]], [[SourceText]] »,the current Realm Record , constructorParent).
- Let defaultConstructor be a new
- Else,
- Let constructorInfo be !
DefineMethod of constructor with arguments proto and constructorParent. - Let F be constructorInfo.[[Closure]].
- Perform
MakeClassConstructor (F). - Perform
SetFunctionName (F, className).
- Let constructorInfo be !
- Perform
MakeConstructor (F,false , proto). - If
ClassHeritage is present, set F.[[ConstructorKind]] toderived . - Perform !
DefineMethodProperty (proto,"constructor" , F,false ). - If
ClassBody is not present, let elements be a new emptyList . - Else, let elements be the
NonConstructorElements ofClassBody . - Let instancePrivateMethods be a new empty
List . - Let staticPrivateMethods be a new empty
List . - Let instanceFields be a new empty
List . - Let staticElements be a new empty
List . - For each
ClassElement e of elements, do- If
IsStatic of e isfalse , then- Let element be
Completion (ClassElementEvaluation of e with argument proto).
- Let element be
- Else,
- Let element be
Completion (ClassElementEvaluation of e with argument F).
- Let element be
- If element is an
abrupt completion , then- Set the
running execution context 's LexicalEnvironment to env. - Set the
running execution context 's PrivateEnvironment to outerPrivateEnvironment. - Return ? element.
- Set the
- Set element to ! element.
- If element is a
PrivateElement , thenAssert : element.[[Kind]] is eithermethod oraccessor .- If
IsStatic of e isfalse , let container be instancePrivateMethods. - Else, let container be staticPrivateMethods.
- If container contains a
PrivateElement pe such that pe.[[Key]] is element.[[Key]], thenAssert : element.[[Kind]] and pe.[[Kind]] are bothaccessor .- If element.[[Get]] is
undefined , then- Let combined be
PrivateElement { [[Key]]: element.[[Key]], [[Kind]]:accessor , [[Get]]: pe.[[Get]], [[Set]]: element.[[Set]] }.
- Let combined be
- Else,
- Let combined be
PrivateElement { [[Key]]: element.[[Key]], [[Kind]]:accessor , [[Get]]: element.[[Get]], [[Set]]: pe.[[Set]] }.
- Let combined be
- Replace pe in container with combined.
- Else,
- Append element to container.
- Else if element is a
ClassFieldDefinition Record , then- If
IsStatic of e isfalse , append element to instanceFields. - Else, append element to staticElements.
- If
- Else if element is a
ClassStaticBlockDefinition Record , then- Append element to staticElements.
- If
- Set the
running execution context 's LexicalEnvironment to env. - If classBinding is not
undefined , then- Perform ! classEnv.InitializeBinding(classBinding, F).
- Set F.[[PrivateMethods]] to instancePrivateMethods.
- Set F.[[Fields]] to instanceFields.
- For each
PrivateElement method of staticPrivateMethods, do- Perform !
PrivateMethodOrAccessorAdd (F, method).
- Perform !
- For each element elementRecord of staticElements, do
- If elementRecord is a
ClassFieldDefinition Record , then- Let result be
Completion (DefineField (F, elementRecord)).
- Let result be
- Else,
Assert : elementRecord is aClassStaticBlockDefinition Record .- Let result be
Completion (Call (elementRecord.[[BodyFunction]], F)).
- If result is an
abrupt completion , then- Set the
running execution context 's PrivateEnvironment to outerPrivateEnvironment. - Return ? result.
- Set the
- If elementRecord is a
- Set the
running execution context 's PrivateEnvironment to outerPrivateEnvironment. - Return F.
15.7.15 Runtime Semantics: BindingClassDeclarationEvaluation
The
- Let className be the
StringValue ofBindingIdentifier . - Let value be ?
ClassDefinitionEvaluation ofClassTail with arguments className and className. - Set value.[[SourceText]] to the
source text matched by ClassDeclaration . - Let env be the
running execution context 's LexicalEnvironment. - Perform ?
InitializeBoundName (className, value, env). - Return value.
- Let value be ?
ClassDefinitionEvaluation ofClassTail with argumentsundefined and"default" . - Set value.[[SourceText]] to the
source text matched by ClassDeclaration . - Return value.
15.7.16 Runtime Semantics: Evaluation
- Perform ?
BindingClassDeclarationEvaluation of thisClassDeclaration . - Return
empty .
- Let value be ?
ClassDefinitionEvaluation ofClassTail with argumentsundefined and"" . - Set value.[[SourceText]] to the
source text matched by ClassExpression . - Return value.
- Let className be the
StringValue ofBindingIdentifier . - Let value be ?
ClassDefinitionEvaluation ofClassTail with arguments className and className. - Set value.[[SourceText]] to the
source text matched by ClassExpression . - Return value.
- Let privateIdentifier be the
StringValue ofPrivateIdentifier . - Let privateEnvRec be the
running execution context 's PrivateEnvironment. - Let names be privateEnvRec.[[Names]].
Assert : Exactly one element of names is aPrivate Name whose [[Description]] is privateIdentifier.- Let privateName be the
Private Name in names whose [[Description]] is privateIdentifier. - Return privateName.
- Return
undefined .
15.8 Async Function Definitions
Syntax
await is parsed as a
- In an
AsyncFunctionBody . - In the
FormalParameters of anAsyncFunctionDeclaration ,AsyncFunctionExpression ,AsyncGeneratorDeclaration , orAsyncGeneratorExpression .AwaitExpression in this position is a Syntax error viastatic semantics . - In a
Module .
When await may
be parsed as an identifier when the [Await] parameter is absent. This includes
the following contexts:
- Anywhere outside of an
AsyncFunctionBody orFormalParameters of anAsyncFunctionDeclaration ,AsyncFunctionExpression ,AsyncGeneratorDeclaration , orAsyncGeneratorExpression . - In the
BindingIdentifier of aFunctionExpression ,GeneratorExpression , orAsyncGeneratorExpression .
Unlike
15.8.1 Static Semantics: Early Errors
- It is a Syntax Error if
FunctionBodyContainsUseStrict ofAsyncFunctionBody istrue andIsSimpleParameterList ofUniqueFormalParameters isfalse . - It is a Syntax Error if
HasDirectSuper ofAsyncMethod istrue . - It is a Syntax Error if
UniqueFormalParameters Contains AwaitExpression istrue . - It is a Syntax Error if any element of the
BoundNames ofUniqueFormalParameters also occurs in theLexicallyDeclaredNames ofAsyncFunctionBody .
- It is a Syntax Error if
FunctionBodyContainsUseStrict ofAsyncFunctionBody istrue andIsSimpleParameterList ofFormalParameters isfalse . - It is a Syntax Error if
FormalParameters Contains AwaitExpression istrue . - If
IsStrict (FormalParameters ) istrue , the Early Error rules forUniqueFormalParameters : FormalParameters - If
BindingIdentifier is present andIsStrict (BindingIdentifier ) istrue , it is a Syntax Error if theStringValue ofBindingIdentifier is either"eval" or"arguments" . - It is a Syntax Error if any element of the
BoundNames ofFormalParameters also occurs in theLexicallyDeclaredNames ofAsyncFunctionBody . - It is a Syntax Error if
FormalParameters Contains SuperProperty istrue . - It is a Syntax Error if
AsyncFunctionBody Contains SuperProperty istrue . - It is a Syntax Error if
FormalParameters Contains SuperCall istrue . - It is a Syntax Error if
AsyncFunctionBody Contains SuperCall istrue .
15.8.2 Runtime Semantics: InstantiateAsyncFunctionObject
The
- Let name be the
StringValue ofBindingIdentifier . - Let sourceText be the
source text matched by AsyncFunctionDeclaration . - Let F be
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F, name). - Return F.
- Let sourceText be the
source text matched by AsyncFunctionDeclaration . - Let F be
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F,"default" ). - Return F.
15.8.3 Runtime Semantics: InstantiateAsyncFunctionExpression
The
- If name is not present, set name to
"" . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncFunctionExpression . - Let closure be
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (closure, name). - Return closure.
Assert : name is not present.- Set name to the
StringValue ofBindingIdentifier . - Let outerEnv be the LexicalEnvironment of the
running execution context . - Let funcEnv be
NewDeclarativeEnvironment (outerEnv). - Perform ! funcEnv.CreateImmutableBinding(name,
false ). - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncFunctionExpression . - Let closure be
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this , funcEnv, privateEnv). - Perform
SetFunctionName (closure, name). - Perform ! funcEnv.InitializeBinding(name, closure).
- Return closure.
The
15.8.4 Runtime Semantics: EvaluateAsyncFunctionBody
The
- Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let completion be
Completion (FunctionDeclarationInstantiation (functionObject, argumentsList)). - If completion is an
abrupt completion , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « completion.[[Value]] »).
- Perform !
- Else,
- Perform
AsyncFunctionStart (promiseCapability,FunctionBody ).
- Perform
- Return
ReturnCompletion (promiseCapability.[[Promise]]).
15.8.5 Runtime Semantics: Evaluation
- Let exprRef be ?
Evaluation ofUnaryExpression . - Let value be ?
GetValue (exprRef). - Return ?
Await (value).
15.9 Async Arrow Function Definitions
Syntax
Supplemental Syntax
When processing an instance of the production
the interpretation of
15.9.1 Static Semantics: Early Errors
- It is a Syntax Error if any element of the
BoundNames ofAsyncArrowBindingIdentifier also occurs in theLexicallyDeclaredNames ofAsyncConciseBody .
CoverCallExpressionAndAsyncArrowHead must cover anAsyncArrowHead .- It is a Syntax Error if
CoverCallExpressionAndAsyncArrowHead Contains YieldExpression istrue . - It is a Syntax Error if
CoverCallExpressionAndAsyncArrowHead Contains AwaitExpression istrue . - It is a Syntax Error if any element of the
BoundNames ofCoverCallExpressionAndAsyncArrowHead also occurs in theLexicallyDeclaredNames ofAsyncConciseBody . - It is a Syntax Error if
AsyncConciseBodyContainsUseStrict ofAsyncConciseBody istrue andIsSimpleParameterList ofCoverCallExpressionAndAsyncArrowHead isfalse .
15.9.2 Static Semantics: AsyncConciseBodyContainsUseStrict
The
- Return
false .
- Return
FunctionBodyContainsUseStrict ofAsyncFunctionBody .
15.9.3 Runtime Semantics: EvaluateAsyncConciseBody
The
- Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let completion be
Completion (FunctionDeclarationInstantiation (functionObject, argumentsList)). - If completion is an
abrupt completion , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « completion.[[Value]] »).
- Perform !
- Else,
- Perform
AsyncFunctionStart (promiseCapability,ExpressionBody ).
- Perform
- Return
ReturnCompletion (promiseCapability.[[Promise]]).
15.9.4 Runtime Semantics: InstantiateAsyncArrowFunctionExpression
The
- If name is not present, set name to
"" . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncArrowFunction . - Let parameters be
AsyncArrowBindingIdentifier . - Let closure be
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText, parameters,AsyncConciseBody ,lexical-this , env, privateEnv). - Perform
SetFunctionName (closure, name). - Return closure.
- If name is not present, set name to
"" . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncArrowFunction . - Let head be the
AsyncArrowHead that iscovered byCoverCallExpressionAndAsyncArrowHead . - Let parameters be the
ArrowFormalParameters of head. - Let closure be
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText, parameters,AsyncConciseBody ,lexical-this , env, privateEnv). - Perform
SetFunctionName (closure, name). - Return closure.
15.9.5 Runtime Semantics: Evaluation
15.10 Tail Position Calls
15.10.1 Static Semantics: IsInTailPosition ( call )
The abstract operation IsInTailPosition takes argument call (a
- If
IsStrict (call) isfalse , returnfalse . - If call is not contained within a
FunctionBody , aConciseBody , or anAsyncConciseBody , returnfalse . - Let body be the
FunctionBody ,ConciseBody , orAsyncConciseBody that most closely contains call. - If body is the
FunctionBody of aGeneratorBody , returnfalse . - If body is the
FunctionBody of anAsyncFunctionBody , returnfalse . - If body is the
FunctionBody of anAsyncGeneratorBody , returnfalse . - If body is an
AsyncConciseBody , returnfalse . - Return the result of
HasCallInTailPosition of body with argument call.
Tail Position calls are only defined in
15.10.2 Static Semantics: HasCallInTailPosition
The
call is a
A potential tail position call that is immediately followed by return
It is defined piecewise over the following productions:
- Let has be
HasCallInTailPosition ofStatementList with argument call. - If has is
true , returntrue . - Return
HasCallInTailPosition ofStatementListItem with argument call.
- Return
false .
- Let has be
HasCallInTailPosition of the firstStatement with argument call. - If has is
true , returntrue . - Return
HasCallInTailPosition of the secondStatement with argument call.
- Return
HasCallInTailPosition ofStatement with argument call.
- Return
HasCallInTailPosition ofLabelledItem with argument call.
- Return
HasCallInTailPosition ofExpression with argument call.
- Return
HasCallInTailPosition ofCaseBlock with argument call.
- Let has be
false . - If the first
CaseClauses is present, set has toHasCallInTailPosition of the firstCaseClauses with argument call. - If has is
true , returntrue . - Set has to
HasCallInTailPosition ofDefaultClause with argument call. - If has is
true , returntrue . - If the second
CaseClauses is present, set has toHasCallInTailPosition of the secondCaseClauses with argument call. - Return has.
- Let has be
HasCallInTailPosition ofCaseClauses with argument call. - If has is
true , returntrue . - Return
HasCallInTailPosition ofCaseClause with argument call.
- If
StatementList is present, returnHasCallInTailPosition ofStatementList with argument call. - Return
false .
- Return
HasCallInTailPosition ofCatch with argument call.
- Return
HasCallInTailPosition ofFinally with argument call.
- Return
HasCallInTailPosition ofBlock with argument call.
- Return
false .
- Return
HasCallInTailPosition ofAssignmentExpression with argument call.
- Let has be
HasCallInTailPosition of the firstAssignmentExpression with argument call. - If has is
true , returntrue . - Return
HasCallInTailPosition of the secondAssignmentExpression with argument call.
- Return
HasCallInTailPosition ofBitwiseORExpression with argument call.
- Return
HasCallInTailPosition ofLogicalANDExpression with argument call.
- Return
HasCallInTailPosition ofBitwiseORExpression with argument call.
- If this
CallExpression is call, returntrue . - Return
false .
- Return
HasCallInTailPosition ofOptionalChain with argument call.
- Return
false .
- If this
OptionalChain is call, returntrue . - Return
false .
- If this
MemberExpression is call, returntrue . - Return
false .
- Let expr be the
ParenthesizedExpression that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return
HasCallInTailPosition of expr with argument call.
- Return
HasCallInTailPosition ofExpression with argument call.
15.10.3 PrepareForTailCall ( )
The abstract operation PrepareForTailCall takes no arguments and returns
Assert : The currentexecution context will not subsequently be used for the evaluation of any ECMAScript code or built-in functions. The invocation of Call subsequent to the invocation of this abstract operation will create and push a newexecution context before performing any such evaluation.- Discard all resources associated with the current
execution context . - Return
unused .
A tail position call must either release any transient internal resources associated with the
currently executing function
For example, a tail position call should only grow an implementation's activation record stack by the amount that the size of the target function's activation record exceeds the size of the calling function's activation record. If the target function's activation record is smaller, then the total size of the stack should decrease.
16 ECMAScript Language: Scripts and Modules
16.1 Scripts
Syntax
16.1.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
LexicallyDeclaredNames ofScriptBody contains any duplicate entries. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofScriptBody also occurs in theVarDeclaredNames ofScriptBody .
-
It is a Syntax Error if
StatementList Contains superunless the source text containingsuperis eval code that is being processed by adirect eval . Additionalearly error rules forsuperwithindirect eval are defined in19.2.1.1 . -
It is a Syntax Error if
StatementList Contains NewTarget unless the source text containingNewTarget is eval code that is being processed by adirect eval . Additionalearly error rules forNewTarget indirect eval are defined in19.2.1.1 . -
It is a Syntax Error if
ContainsDuplicateLabels ofStatementList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedBreakTarget ofStatementList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedContinueTarget ofStatementList with arguments « » and « » istrue . -
It is a Syntax Error if
AllPrivateIdentifiersValid ofStatementList with argument « » isfalse unless the source text containingScriptBody is eval code that is being processed by adirect eval .
16.1.2 Static Semantics: ScriptIsStrict
The
- If
ScriptBody is present and theDirective Prologue ofScriptBody contains aUse Strict Directive , returntrue ; otherwise returnfalse .
16.1.3 Runtime Semantics: Evaluation
- Return
undefined .
16.1.4 Script Records
A Script Record
encapsulates information about a script being evaluated. Each script record contains the fields
listed in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Realm]] |
a |
The |
| [[ECMAScriptCode]] |
a |
The result of parsing the source text of this script. |
| [[LoadedModules]] |
a |
A map from the specifier strings imported by this script to the resolved
|
| [[HostDefined]] |
anything (default value is |
Field reserved for use by |
16.1.5 ParseScript ( sourceText, realm, hostDefined )
The abstract operation ParseScript takes arguments sourceText (
- Let script be
ParseText (sourceText,Script ). - If script is a
List of errors, return script. - Return
Script Record { [[Realm]]: realm, [[ECMAScriptCode]]: script, [[LoadedModules]]: « », [[HostDefined]]: hostDefined }.
An implementation may parse script source text and analyse it for Early Error conditions prior to evaluation of ParseScript for that script source text. However, the reporting of any errors must be deferred until the point where this specification actually performs ParseScript upon that source text.
16.1.6 ScriptEvaluation ( scriptRecord )
The abstract operation ScriptEvaluation takes argument scriptRecord (a
- Let globalEnv be scriptRecord.[[Realm]].[[GlobalEnv]].
- Let scriptContext be a new
ECMAScript code execution context . - Set the Function of scriptContext to
null . - Set the
Realm of scriptContext to scriptRecord.[[Realm]]. - Set the ScriptOrModule of scriptContext to scriptRecord.
- Set the VariableEnvironment of scriptContext to globalEnv.
- Set the LexicalEnvironment of scriptContext to globalEnv.
- Set the PrivateEnvironment of scriptContext to
null . - Suspend the
running execution context . - Push scriptContext onto the
execution context stack ; scriptContext is now therunning execution context . - Let script be scriptRecord.[[ECMAScriptCode]].
- Let result be
Completion (GlobalDeclarationInstantiation (script, globalEnv)). - If result is a
normal completion , then- Set result to
Completion (Evaluation of script). - If result is a
normal completion and result.[[Value]] isempty , then- Set result to
NormalCompletion (undefined ).
- Set result to
- Set result to
- Suspend scriptContext and remove it from the
execution context stack . Assert : Theexecution context stack is not empty.- Resume the context that is now on the top of the
execution context stack as therunning execution context . - Return ? result.
16.1.7 GlobalDeclarationInstantiation ( script, env )
The abstract operation GlobalDeclarationInstantiation takes arguments script (a
When an
It performs the following steps when called:
- Let lexNames be the
LexicallyDeclaredNames of script. - Let varNames be the
VarDeclaredNames of script. - For each element name of lexNames, do
- If
HasLexicalDeclaration (env, name) istrue , throw aSyntaxError exception. - Let hasRestrictedGlobal be ?
HasRestrictedGlobalProperty (env, name). - NOTE: Global
varandfunctionbindings (except those that are introduced by non-strictdirect eval ) are non-configurable and are therefore restricted global properties. - If hasRestrictedGlobal is
true , throw aSyntaxError exception.
- If
- For each element name of varNames, do
- If
HasLexicalDeclaration (env, name) istrue , throw aSyntaxError exception.
- If
- Let varDeclarations be the
VarScopedDeclarations of script. - Let functionsToInitialize be a new empty
List . - Let declaredFunctionNames be a new empty
List . - For each element d of varDeclarations, in reverse
List order, do- If d is not either a
VariableDeclaration , aForBinding , or aBindingIdentifier , thenAssert : d is either aFunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration .- NOTE: If there are multiple function declarations for the same name, the last declaration is used.
- Let fn be the sole element of the
BoundNames of d. - If declaredFunctionNames does not contain fn, then
- Let fnDefinable be ?
CanDeclareGlobalFunction (env, fn). - If fnDefinable is
false , throw aTypeError exception. - Append fn to declaredFunctionNames.
- Insert d as the first element of functionsToInitialize.
- Let fnDefinable be ?
- If d is not either a
- Let declaredVarNames be a new empty
List . - For each element d of varDeclarations, do
- If d is either a
VariableDeclaration , aForBinding , or aBindingIdentifier , then- For each String vn of the
BoundNames of d, do- If declaredFunctionNames does not contain
vn, then
- Let vnDefinable be ?
CanDeclareGlobalVar (env, vn). - If vnDefinable is
false , throw aTypeError exception. - If declaredVarNames does not contain
vn, then
- Append vn to declaredVarNames.
- Let vnDefinable be ?
- If declaredFunctionNames does not contain
vn, then
- For each String vn of the
- If d is either a
- NOTE: No abnormal terminations occur after this algorithm step if the
global object is anordinary object . However, if theglobal object is aProxy exotic object it may exhibit behaviours that cause abnormal terminations in some of the following steps. - NOTE: Annex
B.3.2.2 adds additional steps at this point. - Let lexDeclarations be the
LexicallyScopedDeclarations of script. - Let privateEnv be
null . - For each element d of lexDeclarations, do
- NOTE: Lexically declared names are only instantiated here but not initialized.
- For each element dn of the
BoundNames of d, do- If
IsConstantDeclaration of d istrue , then- Perform ? env.CreateImmutableBinding(dn,
true ).
- Perform ? env.CreateImmutableBinding(dn,
- Else,
- Perform ? env.CreateMutableBinding(dn,
false ).
- Perform ? env.CreateMutableBinding(dn,
- If
- For each
Parse Node f of functionsToInitialize, do- Let fn be the sole element of the
BoundNames of f. - Let fo be
InstantiateFunctionObject of f with arguments env and privateEnv. - Perform ?
CreateGlobalFunctionBinding (env, fn, fo,false ).
- Let fn be the sole element of the
- For each String vn of declaredVarNames, do
- Perform ?
CreateGlobalVarBinding (env, vn,false ).
- Perform ?
- Return
unused .
Unlike explicit var or function declarations, properties that are directly created on the
16.2 Modules
Syntax
16.2.1 Module Semantics
16.2.1.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
LexicallyDeclaredNames ofModuleItemList contains any duplicate entries. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofModuleItemList also occurs in theVarDeclaredNames ofModuleItemList . -
It is a Syntax Error if the
ExportedNames ofModuleItemList contains any duplicate entries. -
It is a Syntax Error if any element of the
ExportedBindings ofModuleItemList does not also occur in either theVarDeclaredNames ofModuleItemList , or theLexicallyDeclaredNames ofModuleItemList . -
It is a Syntax Error if
ModuleItemList Contains super. -
It is a Syntax Error if
ModuleItemList Contains NewTarget . -
It is a Syntax Error if
ContainsDuplicateLabels ofModuleItemList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedBreakTarget ofModuleItemList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedContinueTarget ofModuleItemList with arguments « » and « » istrue . -
It is a Syntax Error if
AllPrivateIdentifiersValid ofModuleItemList with argument « » isfalse .
The duplicate export default
- It is a Syntax Error if
IsStringWellFormedUnicode (SV ofStringLiteral ) isfalse .
16.2.1.2 Static Semantics: ImportedLocalNames ( importEntries )
The abstract operation ImportedLocalNames takes argument importEntries (a
- Let localNames be a new empty
List . - For each
ImportEntry Record i of importEntries, do- Append i.[[LocalName]] to localNames.
- Return localNames.
16.2.1.3 ModuleRequest Records
A ModuleRequest Record represents the request to import a module with given import attributes. It consists of the following fields:
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Specifier]] | a String | The module specifier |
| [[Attributes]] |
a |
The import attributes |
A LoadedModuleRequest Record represents the request to import a module
together with the resulting
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Specifier]] | a String | The module specifier |
| [[Attributes]] |
a |
The import attributes |
| [[Module]] |
a |
The loaded module corresponding to this module request |
An ImportAttribute Record consists of the following fields:
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Key]] | a String | The attribute key |
| [[Value]] | a String | The attribute value |
16.2.1.3.1 ModuleRequestsEqual ( left, right )
The abstract operation ModuleRequestsEqual takes arguments left (a
- If left.[[Specifier]] is not
right.[[Specifier]], return
false . - Let leftAttrs be left.[[Attributes]].
- Let rightAttrs be right.[[Attributes]].
- Let leftAttrsCount be the number of elements in leftAttrs.
- Let rightAttrsCount be the number of elements in rightAttrs.
- If leftAttrsCount ≠ rightAttrsCount, return
false . - For each
ImportAttribute Record l of leftAttrs, do- If rightAttrs does not contain an
ImportAttribute Record r such that l.[[Key]] is r.[[Key]] and l.[[Value]] is r.[[Value]], returnfalse .
- If rightAttrs does not contain an
- Return
true .
16.2.1.4 Static Semantics: ModuleRequests
The
- Return a new empty
List .
- Return the
ModuleRequests ofModuleItem .
- Let requests be the
ModuleRequests ofModuleItemList . - Let additionalRequests be the
ModuleRequests ofModuleItem . - For each
ModuleRequest Record mr of additionalRequests, do- If requests does not contain a
ModuleRequest Record mr2 such thatModuleRequestsEqual (mr, mr2) istrue , then- Append mr to requests.
- If requests does not contain a
- Return requests.
- Return a new empty
List .
- Let specifier be the
SV ofFromClause . - Return a
List whose sole element is theModuleRequest Record { [[Specifier]]: specifier, [[Attributes]]: « » }.
- Let specifier be the
SV ofFromClause . - Let attributes be
WithClauseToAttributes ofWithClause . - Return a
List whose sole element is theModuleRequest Record { [[Specifier]]: specifier, [[Attributes]]: attributes }.
- Let specifier be the
SV ofModuleSpecifier . - Return a
List whose sole element is theModuleRequest Record { [[Specifier]]: specifier, [[Attributes]]: « » }.
- Let specifier be the
SV ofModuleSpecifier . - Let attributes be
WithClauseToAttributes ofWithClause . - Return a
List whose sole element is theModuleRequest Record { [[Specifier]]: specifier, [[Attributes]]: attributes }.
- Let specifier be the
SV ofFromClause . - Return a
List whose sole element is theModuleRequest Record { [[Specifier]]: specifier, [[Attributes]]: « » }.
- Let specifier be the
SV ofFromClause . - Let attributes be
WithClauseToAttributes ofWithClause . - Return a
List whose sole element is theModuleRequest Record { [[Specifier]]: specifier, [[Attributes]]: attributes }.
- Return a new empty
List .
16.2.1.5 Abstract Module Records
A Module Record encapsulates structural information about the imports and exports of a single module. This information is used to link the imports and exports of sets of connected modules. A Module Record includes four fields that are only used when evaluating a module.
For specification purposes Module Record values are values of the
Module Record defines the fields listed in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Realm]] |
a |
The |
| [[Environment]] |
a |
The |
| [[Namespace]] |
an Object or |
The Module Namespace Object ( |
| [[HostDefined]] |
anything (default value is |
Field reserved for use by |
| Method | Purpose |
|---|---|
| LoadRequestedModules([hostDefined]) |
Prepares the module for linking by recursively loading all its dependencies, and returns a promise. |
| GetExportedNames([exportStarSet]) |
Return a list of all names that are either directly or indirectly exported from this module. LoadRequestedModules must have completed successfully prior to invoking this method. |
| ResolveExport(exportName [, resolveSet]) |
Return the binding of a name exported by this module. Bindings are
represented by a ResolvedBinding
Record, of the form { [[Module]]:
Each time this operation is called with a specific exportName, resolveSet pair as arguments it must return the same result. LoadRequestedModules must have completed successfully prior to invoking this method. |
| Link() |
Prepare the module for evaluation by transitively resolving all
module dependencies and creating a LoadRequestedModules must have completed successfully prior to invoking this method. |
| Evaluate() |
Returns a promise for the evaluation of this module and its
dependencies, resolving on successful evaluation or if it has
already been evaluated successfully, and rejecting for an evaluation
error or if it has already been evaluated unsuccessfully. If the
promise is rejected, Link must have completed successfully prior to invoking this method. |
16.2.1.5.1 EvaluateModuleSync ( module )
The abstract operation EvaluateModuleSync takes argument module (a
Assert : module is not aCyclic Module Record .- Let promise be module.Evaluate().
Assert : promise.[[PromiseState]] is eitherfulfilled orrejected .- If promise.[[PromiseState]] is
rejected , then- If promise.[[PromiseIsHandled]] is
false , performHostPromiseRejectionTracker (promise,"handle" ). - Set promise.[[PromiseIsHandled]] to
true . - Return
ThrowCompletion (promise.[[PromiseResult]]).
- If promise.[[PromiseIsHandled]] is
- Return
unused .
16.2.1.6 Cyclic Module Records
A Cyclic Module
Record is used to represent information about a module that can participate in
dependency cycles with other modules that are subclasses of the
In addition to the fields defined in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Status]] |
|
Initially |
| [[EvaluationError]] |
a |
A |
| [[DFSAncestorIndex]] |
an |
Auxiliary field used during Link and Evaluate only. If [[Status]] is either
|
| [[RequestedModules]] |
a |
A |
| [[LoadedModules]] |
a |
A map from the specifier strings used by the module represented by this
record to request the importation of a module with the relative import
attributes to the resolved |
| [[CycleRoot]] |
a |
The first visited module of the cycle, the root DFS ancestor of the strongly connected component. For a module not in a cycle, this would be the module itself. Once Evaluate has completed, a module's [[DFSAncestorIndex]] is the depth-first traversal index of its [[CycleRoot]]. |
| [[HasTLA]] | a Boolean |
Whether this module is individually asynchronous (for example, if it's a
|
| [[AsyncEvaluationOrder]] |
|
This field is initially set to |
| [[TopLevelCapability]] |
a |
If this module is the [[CycleRoot]] of some
cycle, and Evaluate() was called on some module in that cycle, this
field contains the |
| [[AsyncParentModules]] |
a |
If this module or a dependency has [[HasTLA]]
|
| [[PendingAsyncDependencies]] |
an |
If this module has any asynchronous dependencies, this tracks the number of asynchronous dependency modules remaining to execute for this module. A module with asynchronous dependencies will be executed when this field reaches 0 and there are no execution errors. |
In addition to the methods defined in
| Method | Purpose |
|---|---|
| InitializeEnvironment() |
Initialize the |
| ExecuteModule([promiseCapability]) |
Evaluate the module's code within its |
A GraphLoadingState Record is a
| Field Name | Value Type | Meaning |
|---|---|---|
| [[PromiseCapability]] |
a |
The promise to resolve when the loading process finishes. |
| [[IsLoading]] | a Boolean | It is true if the loading process has not finished yet, neither successfully nor with an error. |
| [[PendingModulesCount]] |
a non-negative |
It tracks the number of pending |
| [[Visited]] |
a |
It is a list of the |
| [[HostDefined]] |
anything (default value is |
It contains |
16.2.1.6.1 Implementation of Module Record Abstract Methods
The following are the concrete methods for
16.2.1.6.1.1 LoadRequestedModules ( [ hostDefined ] )
The LoadRequestedModules concrete method of a
- If hostDefined is not present, let hostDefined be
empty . - Let pc be !
NewPromiseCapability (%Promise% ). - Let state be the
GraphLoadingState Record { [[IsLoading]]:true , [[PendingModulesCount]]: 1, [[Visited]]: « », [[PromiseCapability]]: pc, [[HostDefined]]: hostDefined }. - Perform
InnerModuleLoading (state, module). - Return pc.[[Promise]].
<link rel="preload" as="..."> tags.
import() expressions never set the hostDefined
parameter.
16.2.1.6.1.1.1 InnerModuleLoading ( state, module )
The abstract operation InnerModuleLoading takes arguments state (a
Assert : state.[[IsLoading]] istrue .- If module is a
Cyclic Module Record , module.[[Status]] isnew , and state.[[Visited]] does not contain module, then- Append module to state.[[Visited]].
- Let requestedModulesCount be the number of elements in module.[[RequestedModules]].
- Set state.[[PendingModulesCount]] to state.[[PendingModulesCount]] + requestedModulesCount.
- For each
ModuleRequest Record request of module.[[RequestedModules]], do- If
AllImportAttributesSupported (request.[[Attributes]]) isfalse , then- Let error be
ThrowCompletion (a newly createdSyntaxError object). - Perform
ContinueModuleLoading (state, error).
- Let error be
- Else if module.[[LoadedModules]] contains a
LoadedModuleRequest Record record such thatModuleRequestsEqual (record, request) istrue , then- Perform
InnerModuleLoading (state, record.[[Module]]).
- Perform
- Else,
- Perform
HostLoadImportedModule (module, request, state.[[HostDefined]], state). - NOTE:
HostLoadImportedModule will callFinishLoadingImportedModule , which re-enters the graph loading process throughContinueModuleLoading .
- Perform
- If state.[[IsLoading]] is
false , returnunused .
- If
Assert : state.[[PendingModulesCount]] ≥ 1.- Set state.[[PendingModulesCount]] to state.[[PendingModulesCount]] - 1.
- If state.[[PendingModulesCount]] =
0, then
- Set state.[[IsLoading]] to
false . - For each
Cyclic Module Record loaded of state.[[Visited]], do- If loaded.[[Status]]
is
new , set loaded.[[Status]] tounlinked .
- If loaded.[[Status]]
is
- Perform !
Call (state.[[PromiseCapability]].[[Resolve]],undefined , «undefined »).
- Set state.[[IsLoading]] to
- Return
unused .
16.2.1.6.1.1.2 ContinueModuleLoading ( state, moduleCompletion )
The abstract operation ContinueModuleLoading takes arguments state (a
- If state.[[IsLoading]] is
false , returnunused . - If moduleCompletion is a
normal completion , then- Perform
InnerModuleLoading (state, moduleCompletion.[[Value]]).
- Perform
- Else,
- Set state.[[IsLoading]] to
false . - Perform !
Call (state.[[PromiseCapability]].[[Reject]],undefined , « moduleCompletion.[[Value]] »).
- Set state.[[IsLoading]] to
- Return
unused .
16.2.1.6.1.2 Link ( )
The Link concrete method of a
Assert : module.[[Status]] is one ofunlinked ,linked ,evaluating-async , orevaluated .- Let stack be a new empty
List . - Let result be
Completion (InnerModuleLinking (module, stack, 0)). - If result is an
abrupt completion , then- For each
Cyclic Module Record m of stack, doAssert : m.[[Status]] islinking .- Set m.[[Status]] to
unlinked .
Assert : module.[[Status]] isunlinked .- Return ? result.
- For each
Assert : module.[[Status]] is one oflinked ,evaluating-async , orevaluated .Assert : stack is empty.- Return
unused .
16.2.1.6.1.2.1 InnerModuleLinking ( module, stack, index )
The abstract operation InnerModuleLinking takes arguments module (a
- If module is not a
Cyclic Module Record , then- Perform ? module.Link().
- Return index.
- If module.[[Status]] is one of
linking ,linked ,evaluating-async , orevaluated , then- Return index.
Assert : module.[[Status]] isunlinked .- Set module.[[Status]] to
linking . - Let moduleIndex be index.
- Set module.[[DFSAncestorIndex]] to index.
- Set index to index + 1.
- Append module to stack.
- For each
ModuleRequest Record request of module.[[RequestedModules]], do- Let requiredModule be
GetImportedModule (module, request). - Set index to ?
InnerModuleLinking (requiredModule, stack, index). - If requiredModule is a
Cyclic Module Record , thenAssert : requiredModule.[[Status]] is one oflinking ,linked ,evaluating-async , orevaluated .Assert : requiredModule.[[Status]] islinking if and only if stack contains requiredModule.- If requiredModule.[[Status]] is
linking , then- Set module.[[DFSAncestorIndex]] to
min (module.[[DFSAncestorIndex]], requiredModule.[[DFSAncestorIndex]]).
- Set module.[[DFSAncestorIndex]] to
- Let requiredModule be
- Perform ? module.InitializeEnvironment().
Assert : module occurs exactly once in stack.Assert : module.[[DFSAncestorIndex]] ≤ moduleIndex.- If module.[[DFSAncestorIndex]] =
moduleIndex, then
- Let done be
false . - Repeat, while done is
false ,- Let requiredModule be the last element of stack.
- Remove the last element of stack.
Assert : requiredModule is aCyclic Module Record .- Set requiredModule.[[Status]] to
linked . - If requiredModule and module are
the same
Module Record , set done totrue .
- Let done be
- Return index.
16.2.1.6.1.3 Evaluate ( )
The Evaluate concrete method of a
Assert : This call to Evaluate is not happening at the same time as another call to Evaluate within thesurrounding agent .Assert : module.[[Status]] is one oflinked ,evaluating-async , orevaluated .- If module.[[Status]] is either
evaluating-async orevaluated , set module to module.[[CycleRoot]]. - If module.[[TopLevelCapability]] is not
empty , then- Return module.[[TopLevelCapability]].[[Promise]].
- Let stack be a new empty
List . - Let capability be !
NewPromiseCapability (%Promise% ). - Set module.[[TopLevelCapability]] to capability.
- Let result be
Completion (InnerModuleEvaluation (module, stack, 0)). - If result is an
abrupt completion , then- For each
Cyclic Module Record m of stack, do Assert : module.[[Status]] isevaluated .Assert : module.[[EvaluationError]] and result are the sameCompletion Record .- Perform !
Call (capability.[[Reject]],undefined , « result.[[Value]] »).
- For each
- Else,
- Return capability.[[Promise]].
16.2.1.6.1.3.1 InnerModuleEvaluation ( module, stack, index )
The abstract operation InnerModuleEvaluation takes arguments module (a
- If module is not a
Cyclic Module Record , then- Perform ?
EvaluateModuleSync (module). - Return index.
- Perform ?
- If module.[[Status]] is either
evaluating-async orevaluated , then- If module.[[EvaluationError]] is
empty , return index. - Otherwise, return ? module.[[EvaluationError]].
- If module.[[EvaluationError]] is
- If module.[[Status]] is
evaluating , return index. Assert : module.[[Status]] islinked .- Set module.[[Status]] to
evaluating . - Let moduleIndex be index.
- Set module.[[DFSAncestorIndex]] to index.
- Set module.[[PendingAsyncDependencies]] to 0.
- Set index to index + 1.
- Append module to stack.
- For each
ModuleRequest Record request of module.[[RequestedModules]], do- Let requiredModule be
GetImportedModule (module, request). - Set index to ?
InnerModuleEvaluation (requiredModule, stack, index). - If requiredModule is a
Cyclic Module Record , thenAssert : requiredModule.[[Status]] is one ofevaluating ,evaluating-async , orevaluated .Assert : requiredModule.[[Status]] isevaluating if and only if stack contains requiredModule.- If requiredModule.[[Status]] is
evaluating , then- Set module.[[DFSAncestorIndex]] to
min (module.[[DFSAncestorIndex]], requiredModule.[[DFSAncestorIndex]]).
- Set module.[[DFSAncestorIndex]] to
- Else,
- Set requiredModule to requiredModule.[[CycleRoot]].
Assert : requiredModule.[[Status]] is eitherevaluating-async orevaluated .- If requiredModule.[[EvaluationError]] is
not
empty , return ? requiredModule.[[EvaluationError]].
- If requiredModule.[[AsyncEvaluationOrder]] is an
integer , then- Set module.[[PendingAsyncDependencies]] to module.[[PendingAsyncDependencies]] + 1.
- Append module to requiredModule.[[AsyncParentModules]].
- Let requiredModule be
- If module.[[PendingAsyncDependencies]] > 0 or
module.[[HasTLA]] is
true , thenAssert : module.[[AsyncEvaluationOrder]] isunset .- Set module.[[AsyncEvaluationOrder]] to
IncrementModuleAsyncEvaluationCount (). - If module.[[PendingAsyncDependencies]] = 0,
perform
ExecuteAsyncModule (module).
- Else,
- Perform ? module.ExecuteModule().
Assert : module occurs exactly once in stack.Assert : module.[[DFSAncestorIndex]] ≤ moduleIndex.- If module.[[DFSAncestorIndex]] =
moduleIndex, then
- Let done be
false . - Repeat, while done is
false ,- Let requiredModule be the last element of stack.
- Remove the last element of stack.
Assert : requiredModule is aCyclic Module Record .Assert : requiredModule.[[AsyncEvaluationOrder]] is either aninteger orunset .- If requiredModule.[[AsyncEvaluationOrder]] is
unset , set requiredModule.[[Status]] toevaluated . - Otherwise, set requiredModule.[[Status]] to
evaluating-async . - If requiredModule and module are
the same
Module Record , set done totrue . - Set requiredModule.[[CycleRoot]] to module.
- Let done be
- Return index.
A module is
Any modules depending on a module of an asynchronous cycle when that
cycle is not
16.2.1.6.1.3.2 ExecuteAsyncModule ( module )
The abstract operation ExecuteAsyncModule takes argument module (a
Assert : module.[[Status]] is eitherevaluating orevaluating-async .Assert : module.[[HasTLA]] istrue .- Let capability be !
NewPromiseCapability (%Promise% ). - Let fulfilledClosure be a new
Abstract Closure with no parameters that captures module and performs the following steps when called:- Perform
AsyncModuleExecutionFulfilled (module). - Return
NormalCompletion (undefined ).
- Perform
- Let onFulfilled be
CreateBuiltinFunction (fulfilledClosure, 0,"" , « »). - Let rejectedClosure be a new
Abstract Closure with parameters (error) that captures module and performs the following steps when called:- Perform
AsyncModuleExecutionRejected (module, error). - Return
NormalCompletion (undefined ).
- Perform
- Let onRejected be
CreateBuiltinFunction (rejectedClosure, 0,"" , « »). - Perform
PerformPromiseThen (capability.[[Promise]], onFulfilled, onRejected). - Perform ! module.ExecuteModule(capability).
- Return
unused .
16.2.1.6.1.3.3 GatherAvailableAncestors ( module, execList )
The abstract operation GatherAvailableAncestors takes arguments module
(a
- For each
Cyclic Module Record m of module.[[AsyncParentModules]], do- If execList does not contain m and
m.[[CycleRoot]].[[EvaluationError]] is
empty , thenAssert : m.[[Status]] isevaluating-async .Assert : m.[[EvaluationError]] isempty .Assert : m.[[AsyncEvaluationOrder]] is aninteger .Assert : m.[[PendingAsyncDependencies]] > 0.- Set m.[[PendingAsyncDependencies]] to m.[[PendingAsyncDependencies]] - 1.
- If m.[[PendingAsyncDependencies]] =
0, then
- Append m to execList.
- If m.[[HasTLA]] is
false , performGatherAvailableAncestors (m, execList).
- If execList does not contain m and
m.[[CycleRoot]].[[EvaluationError]] is
- Return
unused .
When an asynchronous execution for a root module is fulfilled, this function determines the list of modules which are able to synchronously execute together on this completion, populating them in execList.
16.2.1.6.1.3.4 AsyncModuleExecutionFulfilled ( module )
The abstract operation AsyncModuleExecutionFulfilled takes argument
module (a
- If module.[[Status]] is
evaluated , thenAssert : module.[[EvaluationError]] is notempty .- Return
unused .
Assert : module.[[Status]] isevaluating-async .Assert : module.[[AsyncEvaluationOrder]] is aninteger .Assert : module.[[EvaluationError]] isempty .- Set module.[[AsyncEvaluationOrder]]
to
done . - Set module.[[Status]] to
evaluated . - If module.[[TopLevelCapability]] is
not
empty , thenAssert : module.[[CycleRoot]] and module are the sameModule Record .- Perform !
Call (module.[[TopLevelCapability]].[[Resolve]],undefined , «undefined »).
- Let execList be a new empty
List . - Perform
GatherAvailableAncestors (module, execList). Assert : All elements of execList have their [[AsyncEvaluationOrder]] field set to aninteger , [[PendingAsyncDependencies]] field set to 0, and [[EvaluationError]] field set toempty .- Let sortedExecList be a
List whose elements are the elements of execList, sorted by their [[AsyncEvaluationOrder]] field in ascending order. - For each
Cyclic Module Record m of sortedExecList, do- If m.[[Status]] is
evaluated , thenAssert : m.[[EvaluationError]] is notempty .
- Else if m.[[HasTLA]] is
true , then- Perform
ExecuteAsyncModule (m).
- Perform
- Else,
- Let result be m.ExecuteModule().
- If result is an
abrupt completion , then- Perform
AsyncModuleExecutionRejected (m, result.[[Value]]).
- Perform
- Else,
- Set m.[[AsyncEvaluationOrder]]
to
done . - Set m.[[Status]] to
evaluated . - If m.[[TopLevelCapability]]
is not
empty , thenAssert : m.[[CycleRoot]] and m are the sameModule Record .- Perform !
Call (m.[[TopLevelCapability]].[[Resolve]],undefined , «undefined »).
- Set m.[[AsyncEvaluationOrder]]
to
- If m.[[Status]] is
- Return
unused .
16.2.1.6.1.3.5 AsyncModuleExecutionRejected ( module, error )
The abstract operation AsyncModuleExecutionRejected takes arguments
module (a
- If module.[[Status]] is
evaluated , thenAssert : module.[[EvaluationError]] is notempty .- Return
unused .
Assert : module.[[Status]] isevaluating-async .Assert : module.[[AsyncEvaluationOrder]] is aninteger .Assert : module.[[EvaluationError]] isempty .- Set module.[[EvaluationError]] to
ThrowCompletion (error). - Set module.[[Status]] to
evaluated . - Set module.[[AsyncEvaluationOrder]]
to
done . - NOTE: module.[[AsyncEvaluationOrder]] is set to
done for symmetry withAsyncModuleExecutionFulfilled . InInnerModuleEvaluation , the value of a module's [[AsyncEvaluationOrder]] internal slot is unused when its [[EvaluationError]] internal slot is notempty . - For each
Cyclic Module Record m of module.[[AsyncParentModules]], do- Perform
AsyncModuleExecutionRejected (m, error).
- Perform
- If module.[[TopLevelCapability]] is
not
empty , thenAssert : module.[[CycleRoot]] and module are the sameModule Record .- Perform !
Call (module.[[TopLevelCapability]].[[Reject]],undefined , « error »).
- Return
unused .
16.2.1.6.2 Example Cyclic Module Record Graphs
This non-normative section gives a series of examples of the linking and evaluation of a few common module graphs, with a specific focus on how errors can occur.
First consider the following simple module graph:
Let's first assume that there are no error conditions. When a
Consider then cases involving linking errors, after a successful call to
A.LoadRequestedModules(). If
Finally, consider a case involving evaluation errors after a successful call to Link().
If
Now consider a different type of error condition:
In this scenario, module A declares a dependency on some other module, but no
The difference here between loading, linking and evaluation errors is due to the following characteristic:
Evaluation must be only performed once, as it can cause side effects; it is thus important to remember whether evaluation has already been performed, even if unsuccessfully. (In the error case, it makes sense to also remember the exception because otherwise subsequent Evaluate() calls would have to synthesize a new one.)- Linking, on the other hand, is side-effect-free, and thus even if it fails, it can be retried at a later time with no issues.
- Loading closely interacts with the
host , and it may be desirable for some of them to allow users to retry failed loads (for example, if the failure is caused by temporarily bad network conditions).
Now, consider a module graph with a cycle:
Here we assume that the entry point is module A, so that the
Then the
An analogous story occurs for the evaluation phase of a cyclic module graph, in the success case.
Now consider a case where A has a linking error; for example, it tries to
import a binding from C that does not exist. In that case, the above steps
still occur, including the early return from the second call to
Alternatively, consider a case where A has an evaluation error; for example,
its source code throws an exception. In that case, the evaluation-time analogue of the
above steps still occurs, including the early return from the second call to await through the whole dependency graph
through the
Lastly, consider a module graph with a cycle, where all modules complete asynchronously:
Loading and linking happen as before, and all modules end up with [[Status]] set to
Calling A.Evaluate() calls
|
Field
|
A | B | C | D | E |
|---|---|---|---|---|---|
| [[DFSAncestorIndex]] | 0 | 0 | 0 | 0 | 4 |
| [[Status]] | |||||
| [[AsyncEvaluationOrder]] | 4 | 1 | 3 | 0 | 2 |
| [[AsyncParentModules]] | « » | « A » | « A » | « B, C » | « C » |
| [[PendingAsyncDependencies]] | 2 (B and C) | 1 (D) | 2 (D and E) | 0 | 0 |
Let us assume that E finishes executing first. When that happens,
|
Field
|
C | E |
|---|---|---|
| [[DFSAncestorIndex]] | 0 | 4 |
| [[Status]] | ||
| [[AsyncEvaluationOrder]] | 3 | |
| [[AsyncParentModules]] | « A » | « C » |
| [[PendingAsyncDependencies]] | 1 (D) | 0 |
D is next to finish (as it was the only module that was still executing). When
that happens, await). The fields of the updated modules are as
given in
|
Field
|
B | C | D |
|---|---|---|---|
| [[DFSAncestorIndex]] | 0 | 0 | 0 |
| [[Status]] | |||
| [[AsyncEvaluationOrder]] | 1 | 3 | |
| [[AsyncParentModules]] | « A » | « A » | « B, C » |
| [[PendingAsyncDependencies]] | 0 | 0 | 0 |
Let us assume that C finishes executing next. When that happens,
|
Field
|
A | C |
|---|---|---|
| [[DFSAncestorIndex]] | 0 | 0 |
| [[Status]] | ||
| [[AsyncEvaluationOrder]] | 4 | |
| [[AsyncParentModules]] | « » | « A » |
| [[PendingAsyncDependencies]] | 1 (B) | 0 |
Then, B finishes executing. When that happens,
|
Field
|
A | B |
|---|---|---|
| [[DFSAncestorIndex]] | 0 | 0 |
| [[Status]] | ||
| [[AsyncEvaluationOrder]] | 4 | |
| [[AsyncParentModules]] | « » | « A » |
| [[PendingAsyncDependencies]] | 0 | 0 |
Finally, A finishes executing. When that happens,
|
Field
|
A |
|---|---|
| [[DFSAncestorIndex]] | 0 |
| [[Status]] | |
| [[AsyncEvaluationOrder]] | |
| [[AsyncParentModules]] | « » |
| [[PendingAsyncDependencies]] | 0 |
Alternatively, consider a failure case where C fails execution and returns an
error before B has finished executing. When that happens,
|
Field
|
A | C |
|---|---|---|
| [[DFSAncestorIndex]] | 0 | 0 |
| [[Status]] | ||
| [[AsyncEvaluationOrder]] | ||
| [[AsyncParentModules]] | « » | « A » |
| [[PendingAsyncDependencies]] | 1 (B) | 0 |
| [[EvaluationError]] | C's evaluation error |
A will be rejected with the same error as C since C will
call
|
Field
|
A |
|---|---|
| [[DFSAncestorIndex]] | 0 |
| [[Status]] | |
| [[AsyncEvaluationOrder]] | |
| [[AsyncParentModules]] | « » |
| [[PendingAsyncDependencies]] | 0 |
| [[EvaluationError]] | C's |
Then, B finishes executing without an error. When that happens,
|
Field
|
A | B |
|---|---|---|
| [[DFSAncestorIndex]] | 0 | 0 |
| [[Status]] | ||
| [[AsyncEvaluationOrder]] | 4 | 1 |
| [[AsyncParentModules]] | « » | « A » |
| [[PendingAsyncDependencies]] | 0 | 0 |
| [[EvaluationError]] | C's |
16.2.1.7 Source Text Module Records
A Source
Text Module Record is used to represent information about a module that was
defined from
A
In addition to the fields defined in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[ECMAScriptCode]] |
a |
The result of parsing the source text of this module using |
| [[Context]] |
an |
The |
| [[ImportMeta]] |
an Object or |
An object exposed through the import.meta meta property. It
is |
| [[ImportEntries]] |
a |
A |
| [[LocalExportEntries]] |
a |
A |
| [[IndirectExportEntries]] |
a |
A export * as namespace declarations.
|
| [[StarExportEntries]] |
a |
A export * declarations that occur within the
module, not including export * as namespace declarations.
|
An ImportEntry
Record is a
| Field Name | Value Type | Meaning |
|---|---|---|
| [[ModuleRequest]] |
a |
|
| [[ImportName]] |
a String or |
The name under which the desired binding is exported by the module
identified by [[ModuleRequest]]. The value
|
| [[LocalName]] | a String | The name that is used to locally access the imported value from within the importing module. |
| Import Statement Form | [[ModuleRequest]] | [[ImportName]] | [[LocalName]] |
|---|---|---|---|
import v from "mod";
|
|
|
|
import * as ns from "mod";
|
|
|
|
import {x} from "mod";
|
|
|
|
import {x as v} from "mod";
|
|
|
|
import "mod";
|
An |
||
An ExportEntry
Record is a
| Field Name | Value Type | Meaning |
|---|---|---|
| [[ExportName]] |
a String or |
The name used to export this binding by this module. |
| [[ModuleRequest]] |
a |
The |
| [[ImportName]] |
a String, |
The name under which the desired binding is exported by the module
identified by [[ModuleRequest]].
export * as ns from "mod" declarations.
export * from "mod" declarations.
|
| [[LocalName]] |
a String or |
The name that is used to locally access the exported value from within
the importing module. |
| Export Statement Form | [[ExportName]] | [[ModuleRequest]] | [[ImportName]] | [[LocalName]] |
|---|---|---|---|---|
export var v;
|
|
|
|
|
export default function f() {}
|
|
|
|
|
export default function () {}
|
|
|
|
|
export default 42;
|
|
|
|
|
export {x};
|
|
|
|
|
export {v as x};
|
|
|
|
|
export {x} from "mod";
|
|
|
|
|
export {v as x} from "mod";
|
|
|
|
|
export * from "mod";
|
|
|
|
|
export * as ns from "mod";
|
|
|
|
|
The following definitions specify the required concrete methods and other
16.2.1.7.1 ParseModule ( sourceText, realm, hostDefined )
The abstract operation ParseModule takes arguments sourceText (
- Let body be
ParseText (sourceText,Module ). - If body is a
List of errors, return body. - Let requestedModules be the
ModuleRequests of body. - Let importEntries be the
ImportEntries of body. - Let importedBoundNames be
ImportedLocalNames (importEntries). - Let indirectExportEntries be a new empty
List . - Let localExportEntries be a new empty
List . - Let starExportEntries be a new empty
List . - Let exportEntries be the
ExportEntries of body. - For each
ExportEntry Record ee of exportEntries, do- If ee.[[ModuleRequest]] is
null , then- If importedBoundNames does not contain
ee.[[LocalName]], then
- Append ee to localExportEntries.
- Else,
- Let ie be the element of importEntries whose [[LocalName]] is ee.[[LocalName]].
- If ie.[[ImportName]]
is
namespace-object , then- NOTE: This is a re-export of an imported module namespace object.
- Append ee to localExportEntries.
- Else,
- NOTE: This is a re-export of a single name.
- Append the
ExportEntry Record { [[ModuleRequest]]: ie.[[ModuleRequest]], [[ImportName]]: ie.[[ImportName]], [[LocalName]]:null , [[ExportName]]: ee.[[ExportName]] } to indirectExportEntries.
- If importedBoundNames does not contain
ee.[[LocalName]], then
- Else if ee.[[ImportName]] is
all-but-default , thenAssert : ee.[[ExportName]] isnull .- Append ee to starExportEntries.
- Else,
- Append ee to indirectExportEntries.
- If ee.[[ModuleRequest]] is
- Let async be body
Contains await. - Return
Source Text Module Record { [[Realm]]: realm, [[Environment]]:empty , [[Namespace]]:empty , [[CycleRoot]]:empty , [[HasTLA]]: async, [[AsyncEvaluationOrder]]:unset , [[TopLevelCapability]]:empty , [[AsyncParentModules]]: « », [[PendingAsyncDependencies]]:empty , [[Status]]:new , [[EvaluationError]]:empty , [[HostDefined]]: hostDefined, [[ECMAScriptCode]]: body, [[Context]]:empty , [[ImportMeta]]:empty , [[RequestedModules]]: requestedModules, [[LoadedModules]]: « », [[ImportEntries]]: importEntries, [[LocalExportEntries]]: localExportEntries, [[IndirectExportEntries]]: indirectExportEntries, [[StarExportEntries]]: starExportEntries, [[DFSAncestorIndex]]:empty }.
An implementation may parse module source text and analyse it for Early Error conditions prior to the evaluation of ParseModule for that module source text. However, the reporting of any errors must be deferred until the point where this specification actually performs ParseModule upon that source text.
16.2.1.7.2 Implementation of Module Record Abstract Methods
The following are the concrete methods for
16.2.1.7.2.1 GetExportedNames ( [ exportStarSet ] )
The GetExportedNames concrete method of a
Assert : module.[[Status]] is notnew .- If exportStarSet is not present, set exportStarSet to
a new empty
List . - If exportStarSet contains module, then
- Append module to exportStarSet.
- Let exportedNames be a new empty
List . - For each
ExportEntry Record e of module.[[LocalExportEntries]], do - For each
ExportEntry Record e of module.[[IndirectExportEntries]], do - For each
ExportEntry Record e of module.[[StarExportEntries]], doAssert : e.[[ModuleRequest]] is notnull .- Let requestedModule be
GetImportedModule (module, e.[[ModuleRequest]]). - Let starNames be requestedModule.GetExportedNames(exportStarSet).
- For each element n of starNames, do
- If n is not
"default" , then- If exportedNames does not contain
n, then
- Append n to exportedNames.
- If exportedNames does not contain
n, then
- If n is not
- Return exportedNames.
GetExportedNames does not filter out or throw an exception for names that have ambiguous star export bindings.
16.2.1.7.2.2 ResolveExport ( exportName [ , resolveSet ] )
The ResolveExport concrete method of a
ResolveExport attempts to resolve an imported binding to the actual defining module
and local binding name. The defining module may be the module represented by the
If a defining module is found, a
It performs the following steps when called:
Assert : module.[[Status]] is notnew .- If resolveSet is not present, set resolveSet to a new
empty
List . - For each
Record { [[Module]], [[ExportName]] } r of resolveSet, do- If module and r.[[Module]] are the same
Module Record and exportName is r.[[ExportName]], thenAssert : This is a circular import request.- Return
null .
- If module and r.[[Module]] are the same
- Append the
Record { [[Module]]: module, [[ExportName]]: exportName } to resolveSet. - For each
ExportEntry Record e of module.[[LocalExportEntries]], do- If e.[[ExportName]] is
exportName, then
Assert : module provides the direct binding for this export.- Return
ResolvedBinding Record { [[Module]]: module, [[BindingName]]: e.[[LocalName]] }.
- If e.[[ExportName]] is
exportName, then
- For each
ExportEntry Record e of module.[[IndirectExportEntries]], do- If e.[[ExportName]] is
exportName, then
Assert : e.[[ModuleRequest]] is notnull .- Let importedModule be
GetImportedModule (module, e.[[ModuleRequest]]). - If e.[[ImportName]] is
all , thenAssert : module does not provide the direct binding for this export.- Return
ResolvedBinding Record { [[Module]]: importedModule, [[BindingName]]:namespace }.
- Else,
Assert : module imports a specific binding for this export.Assert : e.[[ImportName]]is a String .- Return importedModule.ResolveExport(e.[[ImportName]], resolveSet).
- If e.[[ExportName]] is
exportName, then
- If exportName is
"default" , thenAssert : Adefaultexport was not explicitly defined by this module.- Return
null . - NOTE: A
defaultexport cannot be provided by anexport * from "mod"declaration.
- Let starResolution be
null . - For each
ExportEntry Record e of module.[[StarExportEntries]], doAssert : e.[[ModuleRequest]] is notnull .- Let importedModule be
GetImportedModule (module, e.[[ModuleRequest]]). - Let resolution be importedModule.ResolveExport(exportName, resolveSet).
- If resolution is
ambiguous , returnambiguous . - If resolution is not
null , thenAssert : resolution is aResolvedBinding Record .- If starResolution is
null , then- Set starResolution to resolution.
- Else,
Assert : There is more than one*import that includes the requested name.- If resolution.[[Module]] and
starResolution.[[Module]] are not the same
Module Record , returnambiguous . - If resolution.[[BindingName]] is not
starResolution.[[BindingName]] and either
resolution.[[BindingName]] or
starResolution.[[BindingName]] is
namespace , returnambiguous . - If resolution.[[BindingName]]
is a String , starResolution.[[BindingName]]is a String , and resolution.[[BindingName]] is not starResolution.[[BindingName]], returnambiguous .
- Return starResolution.
16.2.1.7.3 Implementation of Cyclic Module Record Abstract Methods
The following are the concrete methods for
16.2.1.7.3.1 InitializeEnvironment ( )
The InitializeEnvironment concrete method of a
- For each
ExportEntry Record e of module.[[IndirectExportEntries]], doAssert : e.[[ExportName]] is notnull .- Let resolution be module.ResolveExport(e.[[ExportName]]).
- If resolution is either
null orambiguous , throw aSyntaxError exception. Assert : resolution is aResolvedBinding Record .
Assert : All named exports from module are resolvable.- Let realm be module.[[Realm]].
Assert : realm is notundefined .- Let env be
NewModuleEnvironment (realm.[[GlobalEnv]]). - Set module.[[Environment]] to env.
- For each
ImportEntry Record in of module.[[ImportEntries]], do- Let importedModule be
GetImportedModule (module, in.[[ModuleRequest]]). - If in.[[ImportName]] is
namespace-object , then- Let namespace be
GetModuleNamespace (importedModule). - Perform
! env.CreateImmutableBinding(in.[[LocalName]],
true ). - Perform ! env.InitializeBinding(in.[[LocalName]], namespace).
- Let namespace be
- Else,
- Let resolution be importedModule.ResolveExport(in.[[ImportName]]).
- If resolution is either
null orambiguous , throw aSyntaxError exception. - If resolution.[[BindingName]] is
namespace , then- Let namespace be
GetModuleNamespace (resolution.[[Module]]). - Perform
! env.CreateImmutableBinding(in.[[LocalName]],
true ). - Perform ! env.InitializeBinding(in.[[LocalName]], namespace).
- Let namespace be
- Else,
- Perform
CreateImportBinding (env, in.[[LocalName]], resolution.[[Module]], resolution.[[BindingName]]).
- Perform
- Let importedModule be
- Let moduleContext be a new
ECMAScript code execution context . - Set the Function of moduleContext to
null . Assert : module.[[Realm]] is notundefined .- Set the
Realm of moduleContext to module.[[Realm]]. - Set the ScriptOrModule of moduleContext to module.
- Set the VariableEnvironment of moduleContext to module.[[Environment]].
- Set the LexicalEnvironment of moduleContext to module.[[Environment]].
- Set the PrivateEnvironment of moduleContext to
null . - Set module.[[Context]] to moduleContext.
- Push moduleContext onto the
execution context stack ; moduleContext is now therunning execution context . - Let code be module.[[ECMAScriptCode]].
- Let varDeclarations be the
VarScopedDeclarations of code. - Let declaredVarNames be a new empty
List . - For each element d of varDeclarations, do
- For each element dn of the
BoundNames of d, do- If declaredVarNames does not contain
dn, then
- Perform
! env.CreateMutableBinding(dn,
false ). - Perform
! env.InitializeBinding(dn,
undefined ). - Append dn to declaredVarNames.
- Perform
! env.CreateMutableBinding(dn,
- If declaredVarNames does not contain
dn, then
- For each element dn of the
- Let lexDeclarations be the
LexicallyScopedDeclarations of code. - Let privateEnv be
null . - For each element d of lexDeclarations, do
- For each element dn of the
BoundNames of d, do- If
IsConstantDeclaration of d istrue , then- Perform
! env.CreateImmutableBinding(dn,
true ).
- Perform
! env.CreateImmutableBinding(dn,
- Else,
- Perform
! env.CreateMutableBinding(dn,
false ).
- Perform
! env.CreateMutableBinding(dn,
- If d is either a
FunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration , then- Let fo be
InstantiateFunctionObject of d with arguments env and privateEnv. - Perform ! env.InitializeBinding(dn, fo).
- Let fo be
- If
- For each element dn of the
- Remove moduleContext from the
execution context stack . - Return
unused .
16.2.1.7.3.2 ExecuteModule ( [ capability ] )
The ExecuteModule concrete method of a
- Let moduleContext be a new
ECMAScript code execution context . - Set the Function of moduleContext to
null . - Set the
Realm of moduleContext to module.[[Realm]]. - Set the ScriptOrModule of moduleContext to module.
Assert : module has been linked and declarations in its module environment have been instantiated.- Set the VariableEnvironment of moduleContext to module.[[Environment]].
- Set the LexicalEnvironment of moduleContext to module.[[Environment]].
- Suspend the
running execution context . - If module.[[HasTLA]] is
false , thenAssert : capability is not present.- Push moduleContext onto the
execution context stack ; moduleContext is now therunning execution context . - Let result be
Completion (Evaluation of module.[[ECMAScriptCode]]). - Suspend moduleContext and remove it from the
execution context stack . - Resume the context that is now on the top of the
execution context stack as therunning execution context . - If result is an
abrupt completion , then- Return ? result.
- Else,
Assert : capability is aPromiseCapability Record .- Perform
AsyncBlockStart (capability, module.[[ECMAScriptCode]], moduleContext).
- Return
unused .
16.2.1.8 Synthetic Module Records
A Synthetic Module Record is
used to represent information about a module that is defined by specifications. Its exported
names are statically defined at creation, while their corresponding values can change over
time using
In addition to the fields defined in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[ExportNames]] | a |
The names of the exports of the module. This list does not contain duplicates. |
| [[EvaluationSteps]] | an |
The initialization logic to perform upon evaluation of the module,
taking the |
16.2.1.8.1 CreateDefaultExportSyntheticModule ( defaultExport )
The abstract operation CreateDefaultExportSyntheticModule takes argument
defaultExport (an
- Let realm be
the current Realm Record . - Let setDefaultExport be a new
Abstract Closure with parameters (module) that captures defaultExport and performs the following steps when called:- Perform
SetSyntheticModuleExport (module,"default" , defaultExport). - Return
NormalCompletion (unused ).
- Perform
- Return the
Synthetic Module Record { [[Realm]]: realm, [[Environment]]:empty , [[Namespace]]:empty , [[HostDefined]]:undefined , [[ExportNames]]: «"default" », [[EvaluationSteps]]: setDefaultExport }.
16.2.1.8.2 ParseJSONModule ( source )
The abstract operation ParseJSONModule takes argument source (a String) and
returns either a
- Let json be ?
ParseJSON (source). - Return
CreateDefaultExportSyntheticModule (json).
16.2.1.8.3 SetSyntheticModuleExport ( module, exportName, exportValue )
The abstract operation SetSyntheticModuleExport takes arguments module (a
16.2.1.8.4 Implementation of Module Record Abstract Methods
The following are the concrete methods for
16.2.1.8.4.1 LoadRequestedModules ( )
The LoadRequestedModules concrete method of a
- Return !
PromiseResolve (%Promise% ,undefined ).
16.2.1.8.4.2 GetExportedNames ( )
The GetExportedNames concrete method of a
- Return module.[[ExportNames]].
16.2.1.8.4.3 ResolveExport ( exportName )
The ResolveExport concrete method of a
- If module.[[ExportNames]] does not
contain exportName, return
null . - Return
ResolvedBinding Record { [[Module]]: module, [[BindingName]]: exportName }.
16.2.1.8.4.4 Link ( )
The Link concrete method of a
- Let realm be module.[[Realm]].
- Let env be
NewModuleEnvironment (realm.[[GlobalEnv]]). - Set module.[[Environment]] to env.
- For each String exportName of module.[[ExportNames]], do
- Perform
! env.CreateMutableBinding(exportName,
false ). - Perform
! env.InitializeBinding(exportName,
undefined ).
- Perform
! env.CreateMutableBinding(exportName,
- Return
NormalCompletion (unused ).
16.2.1.8.4.5 Evaluate ( )
The Evaluate concrete method of a
- Let moduleContext be a new
ECMAScript code execution context . - Set the Function of moduleContext to
null . - Set the
Realm of moduleContext to module.[[Realm]]. - Set the ScriptOrModule of moduleContext to module.
- Set the VariableEnvironment of moduleContext to module.[[Environment]].
- Set the LexicalEnvironment of moduleContext to module.[[Environment]].
- Suspend the
running execution context . - Push moduleContext onto the
execution context stack ; moduleContext is now therunning execution context . - Let steps be module.[[EvaluationSteps]].
- Let result be
Completion (steps(module)). - Suspend moduleContext and remove it from the
execution context stack . - Resume the context that is now on the top of the
execution context stack as therunning execution context . - Let pc be !
NewPromiseCapability (%Promise% ). IfAbruptRejectPromise (result, pc).- Perform !
Call (pc.[[Resolve]],undefined , «undefined »). - Return pc.[[Promise]].
16.2.1.9 GetImportedModule ( referrer, request )
The abstract operation GetImportedModule takes arguments referrer (a
- Let records be a
List consisting of eachLoadedModuleRequest Record r of referrer.[[LoadedModules]] such thatModuleRequestsEqual (r, request) istrue . Assert : records has exactly one element, since LoadRequestedModules has completed successfully on referrer prior to invoking this abstract operation.- Let record be the sole element of records.
- Return record.[[Module]].
16.2.1.10 HostLoadImportedModule ( referrer, moduleRequest, hostDefined, payload )
The
An example of when referrer can be a
<button type="button" onclick="import('./foo.mjs')">Click me</button>there will be no import()
An implementation of HostLoadImportedModule must conform to the following requirements:
-
The
host environment must performFinishLoadingImportedModule (referrer, moduleRequest, payload, result), where result is either anormal completion containing the loadedModule Record or athrow completion , either synchronously or asynchronously. -
If this operation is called multiple times with two (referrer, moduleRequest) pairs such that:
- the first referrer is the same as the second referrer;
ModuleRequestsEqual (the first moduleRequest, the second moduleRequest) istrue ;
and it performs
FinishLoadingImportedModule (referrer, moduleRequest, payload, result) where result is anormal completion , then it must performFinishLoadingImportedModule (referrer, moduleRequest, payload, result) with the same result each time. -
If moduleRequest.[[Attributes]] has an entry entry such that entry.[[Key]] is
"type" and entry.[[Value]] is"json" , when thehost environment performsFinishLoadingImportedModule (referrer, moduleRequest, payload, result), result must either be theCompletion Record returned by an invocation ofParseJSONModule or athrow completion . -
The operation must treat payload as an opaque value to be passed through to
FinishLoadingImportedModule .
The actual process performed is
16.2.1.11 FinishLoadingImportedModule ( referrer, moduleRequest, payload, result )
The abstract operation FinishLoadingImportedModule takes arguments referrer (a
- If result is a
normal completion , then- If referrer.[[LoadedModules]] contains a
LoadedModuleRequest Record record such thatModuleRequestsEqual (record, moduleRequest) istrue , thenAssert : record.[[Module]] and result.[[Value]] are the sameModule Record .
- Else,
- Append the
LoadedModuleRequest Record { [[Specifier]]: moduleRequest.[[Specifier]], [[Attributes]]: moduleRequest.[[Attributes]], [[Module]]: result.[[Value]] } to referrer.[[LoadedModules]].
- Append the
- If referrer.[[LoadedModules]] contains a
- If payload is a
GraphLoadingState Record , then- Perform
ContinueModuleLoading (payload, result).
- Perform
- Else,
- Perform
ContinueDynamicImport (payload, result).
- Perform
- Return
unused .
16.2.1.12 AllImportAttributesSupported ( attributes )
The abstract operation AllImportAttributesSupported takes argument attributes (a
- Let supported be
HostGetSupportedImportAttributes (). - For each
ImportAttribute Record attribute of attributes, do- If supported does not contain attribute.[[Key]], return
false .
- If supported does not contain attribute.[[Key]], return
- Return
true .
16.2.1.12.1 HostGetSupportedImportAttributes ( )
The
An implementation of HostGetSupportedImportAttributes must conform to the following requirements:
- It must return a
List of Strings, each indicating a supported attribute. - Each time this operation is called, it must return the same
List with the same contents in the same order.
The default implementation of HostGetSupportedImportAttributes is to return a new empty
16.2.1.13 GetModuleNamespace ( module )
The abstract operation GetModuleNamespace takes argument module (an instance of a
concrete subclass of
Assert : If module is aCyclic Module Record , then module.[[Status]] is notnew orunlinked .- Let namespace be module.[[Namespace]].
- If namespace is
empty , then- Let exportedNames be module.GetExportedNames().
- Let unambiguousNames be a new empty
List . - For each element name of exportedNames, do
- Let resolution be module.ResolveExport(name).
- If resolution is a
ResolvedBinding Record , append name to unambiguousNames.
- Set namespace to
ModuleNamespaceCreate (module, unambiguousNames).
- Return namespace.
GetModuleNamespace never throws. Instead, unresolvable names are simply excluded from the namespace at this point. They will lead to a real linking error later unless they are all ambiguous star exports that are not explicitly requested anywhere.
16.2.1.14 Runtime Semantics: Evaluation
- Return
undefined .
- Let result be
Completion (Evaluation ofModuleItemList ). - If result is a
normal completion and result.[[Value]] isempty , then- Return
undefined .
- Return
- Return ? result.
- Let sl be ?
Evaluation ofModuleItemList . - Let s be
Completion (Evaluation ofModuleItem ). - Return ?
UpdateEmpty (s, sl).
The value of a
- Return
empty .
16.2.2 Imports
Syntax
16.2.2.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
BoundNames ofImportDeclaration contains any duplicate entries.
-
It is a Syntax Error if
WithClauseToAttributes ofWithClause has two different entries a and b such that a.[[Key]] is b.[[Key]].
16.2.2.2 Static Semantics: ImportEntries
The
- Return a new empty
List .
- Let entries1 be the
ImportEntries ofModuleItemList . - Let entries2 be the
ImportEntries ofModuleItem . - Return the
list-concatenation of entries1 and entries2.
- Return a new empty
List .
- Let module be the sole element of the
ModuleRequests ofImportDeclaration . - Return the
ImportEntriesForModule ofImportClause with argument module.
- Return a new empty
List .
16.2.2.3 Static Semantics: ImportEntriesForModule
The
- Let entries1 be the
ImportEntriesForModule ofImportedDefaultBinding with argument module. - Let entries2 be the
ImportEntriesForModule ofNameSpaceImport with argument module. - Return the
list-concatenation of entries1 and entries2.
- Let entries1 be the
ImportEntriesForModule ofImportedDefaultBinding with argument module. - Let entries2 be the
ImportEntriesForModule ofNamedImports with argument module. - Return the
list-concatenation of entries1 and entries2.
- Let localName be the sole element of the
BoundNames ofImportedBinding . - Let defaultEntry be the
ImportEntry Record { [[ModuleRequest]]: module, [[ImportName]]:"default" , [[LocalName]]: localName }. - Return « defaultEntry ».
- Let localName be the
StringValue ofImportedBinding . - Let entry be the
ImportEntry Record { [[ModuleRequest]]: module, [[ImportName]]:namespace-object , [[LocalName]]: localName }. - Return « entry ».
- Return a new empty
List .
- Let specs1 be the
ImportEntriesForModule ofImportsList with argument module. - Let specs2 be the
ImportEntriesForModule ofImportSpecifier with argument module. - Return the
list-concatenation of specs1 and specs2.
- Let localName be the sole element of the
BoundNames ofImportedBinding . - Let entry be the
ImportEntry Record { [[ModuleRequest]]: module, [[ImportName]]: localName, [[LocalName]]: localName }. - Return « entry ».
- Let importName be the
StringValue ofModuleExportName . - Let localName be the
StringValue ofImportedBinding . - Let entry be the
ImportEntry Record { [[ModuleRequest]]: module, [[ImportName]]: importName, [[LocalName]]: localName }. - Return « entry ».
16.2.2.4 Static Semantics: WithClauseToAttributes
The
- Return a new empty
List .
- Let attributes be
WithClauseToAttributes ofWithEntries . - Sort attributes according to the lexicographic order of their [[Key]] field, treating the value of each such field as a
sequence of UTF-16 code unit values. NOTE: This sorting is observable only in that
hosts are prohibited from changing behaviour based on the order in which attributes are enumerated. - Return attributes.
- Let key be the
PropName ofAttributeKey . - Let entry be the
ImportAttribute Record { [[Key]]: key, [[Value]]: theSV ofStringLiteral }. - Return « entry ».
- Let key be the
PropName ofAttributeKey . - Let entry be the
ImportAttribute Record { [[Key]]: key, [[Value]]: theSV ofStringLiteral }. - Let rest be
WithClauseToAttributes ofWithEntries . - Return the
list-concatenation of « entry » and rest.
16.2.3 Exports
Syntax
16.2.3.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
ReferencedBindings ofNamedExports contains anyStringLiteral s. -
For each
IdentifierName n in theReferencedBindings ofNamedExports : It is a Syntax Error if theStringValue of n is aReservedWord or theStringValue of n is one of"implements" ,"interface" ,"let" ,"package" ,"private" ,"protected" ,"public" , or"static" .
The above rule means that each
16.2.3.2 Static Semantics: ExportedBindings
The
ExportedBindings are the locally bound names that are explicitly associated with a
It is defined piecewise over the following productions:
- Let names1 be the
ExportedBindings ofModuleItemList . - Let names2 be the
ExportedBindings ofModuleItem . - Return the
list-concatenation of names1 and names2.
- Return a new empty
List .
- Return a new empty
List .
- Return the
ExportedBindings ofNamedExports .
- Return the
BoundNames ofVariableStatement .
- Return the
BoundNames ofDeclaration .
- Return the
BoundNames of thisExportDeclaration .
- Return a new empty
List .
- Let names1 be the
ExportedBindings ofExportsList . - Let names2 be the
ExportedBindings ofExportSpecifier . - Return the
list-concatenation of names1 and names2.
- Return a
List whose sole element is theStringValue ofModuleExportName .
- Return a
List whose sole element is theStringValue of the firstModuleExportName .
16.2.3.3 Static Semantics: ExportedNames
The
ExportedNames are the externally visible names that a
It is defined piecewise over the following productions:
- Let names1 be the
ExportedNames ofModuleItemList . - Let names2 be the
ExportedNames ofModuleItem . - Return the
list-concatenation of names1 and names2.
- Return the
ExportedNames ofExportDeclaration .
- Return a new empty
List .
- Return the
ExportedNames ofExportFromClause .
- Return a new empty
List .
- Return a
List whose sole element is theStringValue ofModuleExportName .
- Return the
ExportedNames ofNamedExports .
- Return the
BoundNames ofVariableStatement .
- Return the
BoundNames ofDeclaration .
- Return «
"default" ».
- Return a new empty
List .
- Let names1 be the
ExportedNames ofExportsList . - Let names2 be the
ExportedNames ofExportSpecifier . - Return the
list-concatenation of names1 and names2.
- Return a
List whose sole element is theStringValue ofModuleExportName .
- Return a
List whose sole element is theStringValue of the secondModuleExportName .
16.2.3.4 Static Semantics: ExportEntries
The
- Return a new empty
List .
- Let entries1 be the
ExportEntries ofModuleItemList . - Let entries2 be the
ExportEntries ofModuleItem . - Return the
list-concatenation of entries1 and entries2.
- Return a new empty
List .
- Let module be the sole element of the
ModuleRequests ofExportDeclaration . - Return the
ExportEntriesForModule ofExportFromClause with argument module.
- Return the
ExportEntriesForModule ofNamedExports with argumentnull .
- Let entries be a new empty
List . - Let names be the
BoundNames ofVariableStatement . - For each element name of names, do
- Append the
ExportEntry Record { [[ModuleRequest]]:null , [[ImportName]]:null , [[LocalName]]: name, [[ExportName]]: name } to entries.
- Append the
- Return entries.
- Let entries be a new empty
List . - Let names be the
BoundNames ofDeclaration . - For each element name of names, do
- Append the
ExportEntry Record { [[ModuleRequest]]:null , [[ImportName]]:null , [[LocalName]]: name, [[ExportName]]: name } to entries.
- Append the
- Return entries.
- Let names be the
BoundNames ofHoistableDeclaration . - Let localName be the sole element of names.
- Return a
List whose sole element is a newExportEntry Record { [[ModuleRequest]]:null , [[ImportName]]:null , [[LocalName]]: localName, [[ExportName]]:"default" }.
- Let names be the
BoundNames ofClassDeclaration . - Let localName be the sole element of names.
- Return a
List whose sole element is a newExportEntry Record { [[ModuleRequest]]:null , [[ImportName]]:null , [[LocalName]]: localName, [[ExportName]]:"default" }.
- Let entry be the
ExportEntry Record { [[ModuleRequest]]:null , [[ImportName]]:null , [[LocalName]]:"*default*" , [[ExportName]]:"default" }. - Return « entry ».
16.2.3.5 Static Semantics: ExportEntriesForModule
The
- Let entry be the
ExportEntry Record { [[ModuleRequest]]: module, [[ImportName]]:all-but-default , [[LocalName]]:null , [[ExportName]]:null }. - Return « entry ».
- Let exportName be the
StringValue ofModuleExportName . - Let entry be the
ExportEntry Record { [[ModuleRequest]]: module, [[ImportName]]:all , [[LocalName]]:null , [[ExportName]]: exportName }. - Return « entry ».
- Return a new empty
List .
- Let specs1 be the
ExportEntriesForModule ofExportsList with argument module. - Let specs2 be the
ExportEntriesForModule ofExportSpecifier with argument module. - Return the
list-concatenation of specs1 and specs2.
- Let sourceName be the
StringValue ofModuleExportName . - If module is
null , then- Let localName be sourceName.
- Let importName be
null .
- Else,
- Let localName be
null . - Let importName be sourceName.
- Let localName be
- Return a
List whose sole element is a newExportEntry Record { [[ModuleRequest]]: module, [[ImportName]]: importName, [[LocalName]]: localName, [[ExportName]]: sourceName }.
- Let sourceName be the
StringValue of the firstModuleExportName . - Let exportName be the
StringValue of the secondModuleExportName . - If module is
null , then- Let localName be sourceName.
- Let importName be
null .
- Else,
- Let localName be
null . - Let importName be sourceName.
- Let localName be
- Return a
List whose sole element is a newExportEntry Record { [[ModuleRequest]]: module, [[ImportName]]: importName, [[LocalName]]: localName, [[ExportName]]: exportName }.
16.2.3.6 Static Semantics: ReferencedBindings
The
- Return a new empty
List .
- Let names1 be the
ReferencedBindings ofExportsList . - Let names2 be the
ReferencedBindings ofExportSpecifier . - Return the
list-concatenation of names1 and names2.
- Return the
ReferencedBindings of the firstModuleExportName .
- Return a
List whose sole element is theIdentifierName .
- Return a
List whose sole element is theStringLiteral .
16.2.3.7 Runtime Semantics: Evaluation
- Return
empty .
- Return ?
Evaluation ofVariableStatement .
- Return ?
Evaluation ofDeclaration .
- Return ?
Evaluation ofHoistableDeclaration .
- Let value be ?
BindingClassDeclarationEvaluation ofClassDeclaration . - Let className be the sole element of the
BoundNames ofClassDeclaration . - If className is
"*default*" , then- Let env be the
running execution context 's LexicalEnvironment. - Perform ?
InitializeBoundName ("*default*" , value, env).
- Let env be the
- Return
empty .
- If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue , then- Let value be ?
NamedEvaluation ofAssignmentExpression with argument"default" .
- Let value be ?
- Else,
- Let rhs be ?
Evaluation ofAssignmentExpression . - Let value be ?
GetValue (rhs).
- Let rhs be ?
- Let env be the
running execution context 's LexicalEnvironment. - Perform ?
InitializeBoundName ("*default*" , value, env). - Return
empty .
17 Error Handling and Language Extensions
An implementation must report most errors at the time the relevant ECMAScript language construct is
evaluated. An early error is an error
that can be detected and reported prior to the evaluation of any construct in the eval is called and prevent evaluation of the eval
code. All errors that are not
An implementation must report as an
An implementation shall not treat other kinds of errors as
An implementation shall report all errors as specified, except for the following:
-
Except as restricted in
17.1 , ahost or implementation may extendScript syntax,Module syntax, and regular expression pattern or flag syntax. To permit this, all operations (such as callingeval, using a regular expression literal, or using the Function or RegExpconstructor ) that are allowed to throwSyntaxError are permitted to exhibithost-defined behaviour instead of throwingSyntaxError when they encounter ahost-defined extension to the script syntax or regular expression pattern or flag syntax. -
Except as restricted in
17.1 , ahost or implementation may provide additional types, values, objects, properties, and functions beyond those described in this specification. This may cause constructs (such as looking up a variable in the global scope) to havehost-defined behaviour instead of throwing an error (such asReferenceError ).
17.1 Forbidden Extensions
An implementation must not extend this specification in the following ways:
-
ECMAScript
function objects defined using syntacticconstructors instrict mode code must not be created with own properties named"caller" or"arguments" . Such own properties also must not be created forfunction objects defined using anArrowFunction ,MethodDefinition ,GeneratorDeclaration ,GeneratorExpression ,AsyncGeneratorDeclaration ,AsyncGeneratorExpression ,ClassDeclaration ,ClassExpression ,AsyncFunctionDeclaration ,AsyncFunctionExpression , orAsyncArrowFunction regardless of whether the definition is contained instrict mode code . Built-in functions,strict functions created using the Functionconstructor , generator functions created using the Generatorconstructor , async functions created using the AsyncFunctionconstructor , and functions created using thebindmethod also must not be created with such own properties. -
If an implementation extends any
function object with an own property named"caller" the value of that property, as observed using [[Get]] or [[GetOwnProperty]], must not be astrict function object. If it is anaccessor property , the function that is the value of the property's [[Get]] attribute must never return astrict function when called. -
Neither mapped nor unmapped arguments objects may be created with an own property named
"caller" . -
The behaviour of built-in methods which are specified in ECMA-402, such as those named
toLocaleString, must not be extended except as specified in ECMA-402. -
The RegExp pattern grammars in
22.2.1 andB.1.2 must not be extended to recognize any of the source characters A-Z or a-z asIdentityEscape when the [UnicodeMode] grammar parameter is present.[+UnicodeMode] -
The Syntactic Grammar must not be extended in any manner that allows the token
:to immediately follow source text that is matched by theBindingIdentifier nonterminal symbol. -
When processing
strict mode code , an implementation must not relax theearly error rules of12.9.3.1 . -
TemplateEscapeSequence must not be extended to includeLegacyOctalEscapeSequence orNonOctalDecimalEscapeSequence as defined in12.9.4 . -
When processing
strict mode code , the extensions defined inB.3.1 ,B.3.2 ,B.3.3 , andB.3.5 must not be supported. -
When parsing for the
Module goal symbol , the lexical grammar extensions defined inB.1.1 must not be supported. -
ImportCall must not be extended.
18 ECMAScript Standard Built-in Objects
There are certain built-in objects available whenever an ECMAScript
Unless specified otherwise, a built-in object that is callable as a function is a built-in
Many built-in objects are functions: they can be invoked with arguments. Some of them furthermore are
new operator. For each built-in function, this
specification describes the arguments required by that function and the properties of that new expression that invokes that
Unless otherwise specified in the description of a particular function, if a built-in function or
Unless otherwise specified in the description of a particular function, if a built-in function or
Implementations that add additional capabilities to the set of built-in functions are encouraged to do so by adding new functions rather than adding new parameters to existing functions.
Unless otherwise specified every built-in function and every built-in Function.prototype (
Unless otherwise specified every built-in prototype object has the Object.prototype (
If this specification defines a built-in
Built-in
Built-in
Each built-in function defined in this specification is created by calling the
Every built-in
For example, the
Unless otherwise specified, the
Every built-in
The value of the
Unless otherwise specified, the
Every other
Every
19 The Global Object
The global object:
- is created before control enters any
execution context . - does not have a [[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a [[Call]] internal method; it cannot be invoked as a function.
- has a [[Prototype]] internal slot whose value is
host-defined . - may have
host-defined properties in addition to the properties defined in this specification. This may include a property whose value is the global object itself.
19.1 Value Properties of the Global Object
19.1.1 globalThis
The initial value of the
This property has the attributes { [[Writable]]:
19.1.2 Infinity
The value of Infinity is
19.1.3 NaN
The value of NaN is
19.1.4 undefined
The value of undefined is
19.2 Function Properties of the Global Object
19.2.1 eval ( x )
This function is the %eval% intrinsic object.
It performs the following steps when called:
- Return ?
PerformEval (x,false ,false ).
19.2.1.1 PerformEval ( x, strictCaller, direct )
The abstract operation PerformEval takes arguments x (an
Assert : If direct isfalse , then strictCaller is alsofalse .- If x
is not a String , return x. - Let evalRealm be
the current Realm Record . - NOTE: In the case of a
direct eval , evalRealm is therealm of both the caller ofevaland of theevalfunction itself. - Perform ?
HostEnsureCanCompileStrings (evalRealm, « », x, direct). - Let inFunction be
false . - Let inMethod be
false . - Let inDerivedConstructor be
false . - Let inClassFieldInitializer be
false . - If direct is
true , then- Let thisEnvRec be
GetThisEnvironment (). - If thisEnvRec is a
Function Environment Record , then- Let F be thisEnvRec.[[FunctionObject]].
- Set inFunction to
true . - Set inMethod to thisEnvRec.HasSuperBinding().
- If F.[[ConstructorKind]] is
derived , set inDerivedConstructor totrue . - Let classFieldInitializerName be F.[[ClassFieldInitializerName]].
- If classFieldInitializerName is not
empty , set inClassFieldInitializer totrue .
- Let thisEnvRec be
- Perform the following substeps in an
implementation-defined order, possibly interleaving parsing and error detection:- Let script be
ParseText (x,Script ). - If script is a
List of errors, throw aSyntaxError exception. - If script
Contains ScriptBody isfalse , returnundefined . - Let body be the
ScriptBody of script. - If inFunction is
false and bodyContains NewTarget , throw aSyntaxError exception. - If inMethod is
false and bodyContains SuperProperty , throw aSyntaxError exception. - If inDerivedConstructor is
false and bodyContains SuperCall , throw aSyntaxError exception. - If inClassFieldInitializer is
true andContainsArguments of body istrue , throw aSyntaxError exception.
- Let script be
- If strictCaller is
true , let strictEval betrue . - Else, let strictEval be
ScriptIsStrict of script. - Let runningContext be the
running execution context . - NOTE: If direct is
true , runningContext will be theexecution context that performed thedirect eval . If direct isfalse , runningContext will be theexecution context for the invocation of theevalfunction. - If direct is
true , then- Let lexEnv be
NewDeclarativeEnvironment (runningContext's LexicalEnvironment). - Let varEnv be runningContext's VariableEnvironment.
- Let privateEnv be runningContext's PrivateEnvironment.
- Let lexEnv be
- Else,
- Let lexEnv be
NewDeclarativeEnvironment (evalRealm.[[GlobalEnv]]). - Let varEnv be evalRealm.[[GlobalEnv]].
- Let privateEnv be
null .
- Let lexEnv be
- If strictEval is
true , set varEnv to lexEnv. - If runningContext is not already suspended, suspend runningContext.
- Let evalContext be a new
ECMAScript code execution context . - Set evalContext's Function to
null . - Set evalContext's
Realm to evalRealm. - Set evalContext's ScriptOrModule to runningContext's ScriptOrModule.
- Set evalContext's VariableEnvironment to varEnv.
- Set evalContext's LexicalEnvironment to lexEnv.
- Set evalContext's PrivateEnvironment to privateEnv.
- Push evalContext onto the
execution context stack ; evalContext is now therunning execution context . - Let result be
Completion (EvalDeclarationInstantiation (body, varEnv, lexEnv, privateEnv, strictEval)). - If result is a
normal completion , then- Set result to
Completion (Evaluation of body).
- Set result to
- If result is a
normal completion and result.[[Value]] isempty , then- Set result to
NormalCompletion (undefined ).
- Set result to
- Suspend evalContext and remove it from the
execution context stack . - Resume the context that is now on the top of the
execution context stack as therunning execution context . - Return ? result.
The eval code cannot instantiate variable or function bindings in the variable
environment of the calling context that invoked the eval if either the code of the
calling context or the eval code is let,
const, or class declarations are always instantiated in a
new LexicalEnvironment.
19.2.1.2 HostEnsureCanCompileStrings ( calleeRealm, parameterStrings, bodyString, direct )
The
parameterStrings represents the strings that, when using one of the function
eval call.
direct signifies whether the evaluation is a
The default implementation of HostEnsureCanCompileStrings is to return
19.2.1.3 EvalDeclarationInstantiation ( body, varEnv, lexEnv, privateEnv, strict )
The abstract operation EvalDeclarationInstantiation takes arguments body (a
- Let varNames be the
VarDeclaredNames of body. - Let varDeclarations be the
VarScopedDeclarations of body. - If strict is
false , then- If varEnv is a
Global Environment Record , then- For each element name of varNames, do
- If
HasLexicalDeclaration (varEnv, name) istrue , throw aSyntaxError exception. - NOTE:
evalwill not create a global var declaration that would be shadowed by a global lexical declaration.
- If
- For each element name of varNames, do
- Let thisEnv be lexEnv.
Assert : The following loop will terminate.- Repeat, while thisEnv and varEnv are not the same
Environment Record ,- If thisEnv
is not an Object Environment Record , then- NOTE: The environment of with statements cannot contain any lexical declaration so it doesn't need to be checked for var/let hoisting conflicts.
- For each element name of varNames, do
- If
! thisEnv.HasBinding(name)
is
true , then-
Throw a
SyntaxError exception. - NOTE: Annex
B.3.4 defines alternate semantics for the above step.
-
Throw a
- NOTE: A
direct eval will not hoist var declaration over a like-named lexical declaration.
- If
! thisEnv.HasBinding(name)
is
- Set thisEnv to thisEnv.[[OuterEnv]].
- If thisEnv
- If varEnv is a
- Let privateIdentifiers be a new empty
List . - Let pointer be privateEnv.
- Repeat, while pointer is not
null ,- For each
Private Name binding of pointer.[[Names]], do- If privateIdentifiers does not contain binding.[[Description]], append binding.[[Description]] to privateIdentifiers.
- Set pointer to pointer.[[OuterPrivateEnvironment]].
- For each
- If
AllPrivateIdentifiersValid of body with argument privateIdentifiers isfalse , throw aSyntaxError exception. - Let functionsToInitialize be a new empty
List . - Let declaredFunctionNames be a new empty
List . - For each element d of varDeclarations, in reverse
List order, do- If d is not either a
VariableDeclaration , aForBinding , or aBindingIdentifier , thenAssert : d is either aFunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration .- NOTE: If there are multiple function declarations for the same name, the last declaration is used.
- Let fn be the sole element of the
BoundNames of d. - If declaredFunctionNames does not contain fn,
then
- If varEnv is a
Global Environment Record , then- Let fnDefinable be ?
CanDeclareGlobalFunction (varEnv, fn). - If fnDefinable is
false , throw aTypeError exception.
- Let fnDefinable be ?
- Append fn to declaredFunctionNames.
- Insert d as the first element of functionsToInitialize.
- If varEnv is a
- If d is not either a
- Let declaredVarNames be a new empty
List . - For each element d of varDeclarations, do
- If d is either a
VariableDeclaration , aForBinding , or aBindingIdentifier , then- For each String vn of the
BoundNames of d, do- If declaredFunctionNames does not contain
vn, then
- If varEnv is a
Global Environment Record , then- Let vnDefinable be
?
CanDeclareGlobalVar (varEnv, vn). - If vnDefinable is
false , throw aTypeError exception.
- Let vnDefinable be
?
- If declaredVarNames does not contain
vn, then
- Append vn to declaredVarNames.
- If varEnv is a
- If declaredFunctionNames does not contain
vn, then
- For each String vn of the
- If d is either a
- NOTE: Annex
B.3.2.3 adds additional steps at this point. - NOTE: No abnormal
terminations occur after this algorithm step unless varEnv is a
Global Environment Record and theglobal object is aProxy exotic object . - Let lexDeclarations be the
LexicallyScopedDeclarations of body. - For each element d of lexDeclarations, do
- NOTE: Lexically declared names are only instantiated here but not initialized.
- For each element dn of the
BoundNames of d, do- If
IsConstantDeclaration of d istrue , then- Perform
? lexEnv.CreateImmutableBinding(dn,
true ).
- Perform
? lexEnv.CreateImmutableBinding(dn,
- Else,
- Perform
? lexEnv.CreateMutableBinding(dn,
false ).
- Perform
? lexEnv.CreateMutableBinding(dn,
- If
- For each
Parse Node f of functionsToInitialize, do- Let fn be the sole element of the
BoundNames of f. - Let fo be
InstantiateFunctionObject of f with arguments lexEnv and privateEnv. - If varEnv is a
Global Environment Record , then- Perform ?
CreateGlobalFunctionBinding (varEnv, fn, fo,true ).
- Perform ?
- Else,
- Let bindingExists be ! varEnv.HasBinding(fn).
- If bindingExists is
false , then- NOTE: The following invocation cannot return an
abrupt completion because of the validation preceding step14 . - Perform
! varEnv.CreateMutableBinding(fn,
true ). - Perform ! varEnv.InitializeBinding(fn, fo).
- NOTE: The following invocation cannot return an
- Else,
- Perform
! varEnv.SetMutableBinding(fn,
fo,
false ).
- Perform
! varEnv.SetMutableBinding(fn,
fo,
- Let fn be the sole element of the
- For each String vn of declaredVarNames, do
- If varEnv is a
Global Environment Record , then- Perform ?
CreateGlobalVarBinding (varEnv, vn,true ).
- Perform ?
- Else,
- Let bindingExists be ! varEnv.HasBinding(vn).
- If bindingExists is
false , then- NOTE: The following invocation cannot return an
abrupt completion because of the validation preceding step14 . - Perform
! varEnv.CreateMutableBinding(vn,
true ). - Perform
! varEnv.InitializeBinding(vn,
undefined ).
- NOTE: The following invocation cannot return an
- If varEnv is a
- Return
unused .
An alternative version of this algorithm is described in
19.2.2 isFinite ( number )
This function is the %isFinite% intrinsic object.
It performs the following steps when called:
19.2.3 isNaN ( number )
This function is the %isNaN% intrinsic object.
It performs the following steps when called:
- Let num be ?
ToNumber (number). - If num is
NaN , returntrue . - Otherwise, return
false .
A reliable way for ECMAScript code to test if a value X is
X !== X. The result
will be X is
19.2.4 parseFloat ( string )
This function produces a Number value dictated by interpretation of the contents of the string argument as a decimal literal.
It is the %parseFloat% intrinsic object.
It performs the following steps when called:
- Let inputString be ?
ToString (string). - Let trimmedString be !
TrimString (inputString,start ). - Let trimmed be
StringToCodePoints (trimmedString). - Let trimmedPrefix be the longest prefix of trimmed that satisfies
the syntax of a
StrDecimalLiteral , which might be trimmed itself. If there is no such prefix, returnNaN . - Let parsedNumber be
ParseText (trimmedPrefix,StrDecimalLiteral ). Assert : parsedNumber is aParse Node .- Return the
StringNumericValue of parsedNumber.
This function may interpret only a leading portion of string as a Number value; it ignores any code units that cannot be interpreted as part of the notation of a decimal literal, and no indication is given that any such code units were ignored.
19.2.5 parseInt ( string, radix )
This function produces an
It is the %parseInt% intrinsic object.
It performs the following steps when called:
- Let inputString be ?
ToString (string). - Let S be !
TrimString (inputString,start ). - Let sign be 1.
- If S is not empty and the first code unit of S is the code unit 0x002D (HYPHEN-MINUS), set sign to -1.
- If S is not empty and the first code unit of S is either the code
unit 0x002B (PLUS SIGN) or the code unit 0x002D (HYPHEN-MINUS), set S to the
substring of S from index 1. - Let R be
ℝ (?ToInt32 (radix)). - Let stripPrefix be
true . - If R ≠ 0, then
- If R < 2 or R > 36, return
NaN . - If R ≠ 16, set stripPrefix to
false .
- If R < 2 or R > 36, return
- Else,
- Set R to 10.
- If stripPrefix is
true , then- If the length of S is at least 2 and the first two code units of
S are either
"0x" or"0X" , then- Set S to the
substring of S from index 2. - Set R to 16.
- Set S to the
- If the length of S is at least 2 and the first two code units of
S are either
- If S contains a code unit that is not a radix-R digit, let end be the index within S of the first such code unit; otherwise let end be the length of S.
- Let Z be the
substring of S from 0 to end. - If Z is empty, return
NaN . - Let mathInt be the
integer value that is represented by Z in radix-R notation, using the letters A through Z and a through z for digits with values 10 through 35. (However, if R = 10 and Z contains more than 20 significant digits, every significant digit after the 20th may be replaced by a 0 digit, at the option of the implementation; and if R is not one of 2, 4, 8, 10, 16, or 32, then mathInt may be animplementation-approximated integer representing theinteger value denoted by Z in radix-R notation.) - If mathInt = 0, then
- If sign = -1, return
-0 𝔽. - Return
+0 𝔽.
- If sign = -1, return
- Return
𝔽 (sign × mathInt).
19.2.6 URI Handling Functions
Uniform Resource Identifiers, or URIs, are Strings that identify resources (e.g. web pages or
files) and transport protocols by which to access them (e.g. HTTP or FTP) on the Internet. The
ECMAScript language itself does not provide any support for using URIs except for functions that
encode and decode URIs as described in this section. encodeURI and
decodeURI are intended to work with complete URIs; they assume that any reserved
characters are intended to have special meaning (e.g., as delimiters) and so are not encoded.
encodeURIComponent and decodeURIComponent are intended to work with
the individual components of a URI; they assume that any reserved characters represent text and
must be encoded to avoid special meaning when the component is part of a complete URI.
The set of reserved characters is based upon RFC 2396 and does not reflect changes introduced by the more recent RFC 3986.
Many implementations of ECMAScript provide additional functions and methods that manipulate web pages; these functions are beyond the scope of this standard.
19.2.6.1 decodeURI ( encodedURI )
This function computes a new version of a URI in which each escape sequence and UTF-8
encoding of the sort that might be introduced by the encodeURI function is
replaced with the UTF-16 encoding of the code point that it represents. Escape sequences
that could not have been introduced by encodeURI are not replaced.
It is the %decodeURI% intrinsic object.
It performs the following steps when called:
19.2.6.2 decodeURIComponent ( encodedURIComponent )
This function computes a new version of a URI in which each escape sequence and UTF-8
encoding of the sort that might be introduced by the encodeURIComponent
function is replaced with the UTF-16 encoding of the code point that it represents.
It is the %decodeURIComponent% intrinsic object.
It performs the following steps when called:
19.2.6.3 encodeURI ( uri )
This function computes a new version of a UTF-16 encoded (
It is the %encodeURI% intrinsic object.
It performs the following steps when called:
19.2.6.4 encodeURIComponent ( uriComponent )
This function computes a new version of a UTF-16 encoded (
It is the %encodeURIComponent% intrinsic object.
It performs the following steps when called:
19.2.6.5 Encode ( string, extraUnescaped )
The abstract operation Encode takes arguments string (a String) and
extraUnescaped (a String) and returns either a
- Let len be the length of string.
- Let R be the empty String.
- Let alwaysUnescaped be the
string-concatenation ofthe ASCII word characters and"-.!~*'()" . - Let unescapedSet be the
string-concatenation of alwaysUnescaped and extraUnescaped. - Let k be 0.
- Repeat, while k < len,
- Let C be the code unit at index k within string.
- If unescapedSet contains C, then
- Set k to k + 1.
- Set R to the
string-concatenation of R and C.
- Else,
- Let cp be
CodePointAt (string, k). - If cp.[[IsUnpairedSurrogate]] is
true , throw aURIError exception. - Set k to k + cp.[[CodeUnitCount]].
- Let Octets be the
List of octets resulting by applying the UTF-8 transformation to cp.[[CodePoint]]. - For each element octet of Octets, do
- Let hex be the String representation of octet, formatted as an uppercase hexadecimal number.
- Set R to the
string-concatenation of R,"%" , andStringPad (hex, 2,"0" ,start ).
- Let cp be
- Return R.
Because percent-encoding is used to represent individual octets, a single code point may be expressed as multiple consecutive escape sequences (one for each of its 8-bit UTF-8 code units).
19.2.6.6 Decode ( string, preserveEscapeSet )
The abstract operation Decode takes arguments string (a String) and
preserveEscapeSet (a String) and returns either a
- Let len be the length of string.
- Let R be the empty String.
- Let k be 0.
- Repeat, while k < len,
- Let C be the code unit at index k within string.
- Let S be C.
- If C is the code unit 0x0025 (PERCENT SIGN), then
- If k + 3 > len, throw a
URIError exception. - Let escape be the
substring of string from k to k + 3. - Let B be
ParseHexOctet (string, k + 1). - If B is not an
integer , throw aURIError exception. - Set k to k + 2.
- Let n be the number of leading 1 bits in B.
- If n = 0, then
- Let asciiChar be the code unit whose numeric value is B.
- If preserveEscapeSet contains asciiChar, set S to escape; otherwise set S to asciiChar.
- Else,
- If n = 1 or n > 4, throw a
URIError exception. - Let Octets be « B ».
- Let j be 1.
- Repeat, while j < n,
- Set k to k + 1.
- If k + 3 > len, throw a
URIError exception. - If the code unit at index k within
string is not the code unit 0x0025
(PERCENT SIGN), throw a
URIError exception. - Let continuationByte be
ParseHexOctet (string, k + 1). - If continuationByte is not an
integer , throw aURIError exception. - Append continuationByte to Octets.
- Set k to k + 2.
- Set j to j + 1.
Assert : The length of Octets is n.- If Octets does not contain a valid UTF-8 encoding
of a Unicode code point, throw a
URIError exception. - Let V be the code point obtained by applying the
UTF-8 transformation to Octets, that is, from a
List of octets into a 21-bit value. - Set S to
UTF16EncodeCodePoint (V).
- If n = 1 or n > 4, throw a
- If k + 3 > len, throw a
- Set R to the
string-concatenation of R and S. - Set k to k + 1.
- Return R.
RFC 3629 prohibits the decoding of invalid UTF-8 octet sequences. For example, the
invalid sequence 0xC0 0x80 must not decode into the code unit 0x0000.
Implementations of the Decode algorithm are required to throw a
19.2.6.7 ParseHexOctet ( string, position )
The abstract operation ParseHexOctet takes arguments string (a String) and
position (a non-negative
- Let len be the length of string.
Assert : position + 2 ≤ len.- Let hexDigits be the
substring of string from position to position + 2. - Let parseResult be
ParseText (hexDigits,HexDigits ).[~Sep] - If parseResult is not a
Parse Node , return parseResult. - Let n be the MV of parseResult.
Assert : n is in theinclusive interval from 0 to 255.- Return n.
19.3 Constructor Properties of the Global Object
19.3.1 AggregateError ( . . . )
See
19.3.2 Array ( . . . )
See
19.3.3 ArrayBuffer ( . . . )
See
19.3.4 BigInt ( . . . )
See
19.3.5 BigInt64Array ( . . . )
See
19.3.6 BigUint64Array ( . . . )
See
19.3.7 Boolean ( . . . )
See
19.3.8 DataView ( . . . )
See
19.3.9 Date ( . . . )
See
19.3.10 Error ( . . . )
See
19.3.11 EvalError ( . . . )
See
19.3.12 FinalizationRegistry ( . . . )
See
19.3.13 Float16Array ( . . . )
See
19.3.14 Float32Array ( . . . )
See
19.3.15 Float64Array ( . . . )
See
19.3.16 Function ( . . . )
See
19.3.17 Int8Array ( . . . )
See
19.3.18 Int16Array ( . . . )
See
19.3.19 Int32Array ( . . . )
See
19.3.20 Iterator ( . . . )
See
19.3.21 Map ( . . . )
See
19.3.22 Number ( . . . )
See
19.3.23 Object ( . . . )
See
19.3.24 Promise ( . . . )
See
19.3.25 Proxy ( . . . )
See
19.3.26 RangeError ( . . . )
See
19.3.27 ReferenceError ( . . . )
See
19.3.28 RegExp ( . . . )
See
19.3.29 Set ( . . . )
See
19.3.30 SharedArrayBuffer ( . . . )
See
19.3.31 String ( . . . )
See
19.3.32 Symbol ( . . . )
See
19.3.33 SyntaxError ( . . . )
See
19.3.34 TypeError ( . . . )
See
19.3.35 Uint8Array ( . . . )
See
19.3.36 Uint8ClampedArray ( . . . )
See
19.3.37 Uint16Array ( . . . )
See
19.3.38 Uint32Array ( . . . )
See
19.3.39 URIError ( . . . )
See
19.3.40 WeakMap ( . . . )
See
19.3.41 WeakRef ( . . . )
See
19.3.42 WeakSet ( . . . )
See
19.4 Other Properties of the Global Object
19.4.1 Atomics
See
19.4.2 JSON
See
19.4.3 Math
See
19.4.4 Reflect
See
20 Fundamental Objects
20.1 Object Objects
20.1.1 The Object Constructor
The Object
- is %Object%.
- is the initial value of the
"Object" property of theglobal object . - creates a new
ordinary object when called as aconstructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition.
20.1.1.1 Object ( [ value ] )
This function performs the following steps when called:
- If NewTarget is neither
undefined nor theactive function object , then- Return ?
OrdinaryCreateFromConstructor (NewTarget,"%Object.prototype%" ).
- Return ?
- If value is either
undefined ornull , returnOrdinaryObjectCreate (%Object.prototype% ). - Return !
ToObject (value).
20.1.2 Properties of the Object Constructor
The Object
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"length" property whose value is1 𝔽. - has the following additional properties:
20.1.2.1 Object.assign ( target, ...sources )
This function copies the values of all of the enumerable own properties from one or more source objects to a target object.
It performs the following steps when called:
The
20.1.2.2 Object.create ( O, Properties )
This function creates a new object with a specified prototype.
It performs the following steps when called:
- If O
is not an Object and O is notnull , throw aTypeError exception. - Let obj be
OrdinaryObjectCreate (O). - If Properties is not
undefined , then- Return ?
ObjectDefineProperties (obj, Properties).
- Return ?
- Return obj.
20.1.2.3 Object.defineProperties ( O, Properties )
This function adds own properties and/or updates the attributes of existing own properties of an object.
It performs the following steps when called:
- If O
is not an Object , throw aTypeError exception. - Return ?
ObjectDefineProperties (O, Properties).
20.1.2.3.1 ObjectDefineProperties ( O, Properties )
The abstract operation ObjectDefineProperties takes arguments O (an Object)
and Properties (an
- Let props be ?
ToObject (Properties). - Let keys be ? props.[[OwnPropertyKeys]]().
- Let descriptors be a new empty
List . - For each element nextKey of keys, do
- Let propDesc be ? props.[[GetOwnProperty]](nextKey).
- If propDesc is not
undefined and propDesc.[[Enumerable]] istrue , then- Let descObj be ?
Get (props, nextKey). - Let desc be ?
ToPropertyDescriptor (descObj). - Append the
Record { [[Key]]: nextKey, [[Descriptor]]: desc } to descriptors.
- Let descObj be ?
- For each element property of descriptors, do
- Perform ?
DefinePropertyOrThrow (O, property.[[Key]], property.[[Descriptor]]).
- Perform ?
- Return O.
20.1.2.4 Object.defineProperty ( O, P, Attributes )
This function adds an own property and/or updates the attributes of an existing own property of an object.
It performs the following steps when called:
- If O
is not an Object , throw aTypeError exception. - Let key be ?
ToPropertyKey (P). - Let desc be ?
ToPropertyDescriptor (Attributes). - Perform ?
DefinePropertyOrThrow (O, key, desc). - Return O.
20.1.2.5 Object.entries ( O )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let entryList be ?
EnumerableOwnProperties (obj,key+value ). - Return
CreateArrayFromList (entryList).
20.1.2.6 Object.freeze ( O )
This function performs the following steps when called:
- If O
is not an Object , return O. - Let status be ?
SetIntegrityLevel (O,frozen ). - If status is
false , throw aTypeError exception. - Return O.
20.1.2.7 Object.fromEntries ( iterable )
This function performs the following steps when called:
- Perform ?
RequireObjectCoercible (iterable). - Let obj be
OrdinaryObjectCreate (%Object.prototype% ). Assert : obj is an extensibleordinary object with no own properties.- Let closure be a new
Abstract Closure with parameters (key, value) that captures obj and performs the following steps when called:- Let propertyKey be ?
ToPropertyKey (key). - Perform !
CreateDataPropertyOrThrow (obj, propertyKey, value). - Return
NormalCompletion (undefined ).
- Let propertyKey be ?
- Let adder be
CreateBuiltinFunction (closure, 2,"" , « »). - Return ?
AddEntriesFromIterable (obj, iterable, adder).
20.1.2.8 Object.getOwnPropertyDescriptor ( O, P )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let key be ?
ToPropertyKey (P). - Let desc be ? obj.[[GetOwnProperty]](key).
- Return
FromPropertyDescriptor (desc).
20.1.2.9 Object.getOwnPropertyDescriptors ( O )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let ownKeys be ? obj.[[OwnPropertyKeys]]().
- Let descriptors be
OrdinaryObjectCreate (%Object.prototype% ). - For each element key of ownKeys, do
- Let desc be ? obj.[[GetOwnProperty]](key).
- Let descriptor be
FromPropertyDescriptor (desc). - If descriptor is not
undefined , perform !CreateDataPropertyOrThrow (descriptors, key, descriptor).
- Return descriptors.
20.1.2.10 Object.getOwnPropertyNames ( O )
This function performs the following steps when called:
- Return
CreateArrayFromList (?GetOwnPropertyKeys (O,string )).
20.1.2.11 Object.getOwnPropertySymbols ( O )
This function performs the following steps when called:
- Return
CreateArrayFromList (?GetOwnPropertyKeys (O,symbol )).
20.1.2.11.1 GetOwnPropertyKeys ( O, type )
The abstract operation GetOwnPropertyKeys takes arguments O (an
- Let obj be ?
ToObject (O). - Let keys be ? obj.[[OwnPropertyKeys]]().
- Let nameList be a new empty
List . - For each element nextKey of keys, do
- If nextKey
is a Symbol and type issymbol , or if nextKeyis a String and type isstring , then- Append nextKey to nameList.
- If nextKey
- Return nameList.
20.1.2.12 Object.getPrototypeOf ( O )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Return ? obj.[[GetPrototypeOf]]().
20.1.2.13 Object.groupBy ( items, callback )
callback should be a function that accepts two arguments.
groupBy calls callback once for each element in
items, in ascending order, and constructs a new object. Each value
returned by callback is coerced to a
callback is called with two arguments: the value of the element and the index of the element.
The return value of groupBy is an object that does not inherit from
This function performs the following steps when called:
- Let groups be ?
GroupBy (items, callback,property ). - Let obj be
OrdinaryObjectCreate (null ). - For each
Record { [[Key]], [[Elements]] } g of groups, do- Let elements be
CreateArrayFromList (g.[[Elements]]). - Perform !
CreateDataPropertyOrThrow (obj, g.[[Key]], elements).
- Let elements be
- Return obj.
20.1.2.14 Object.hasOwn ( O, P )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let key be ?
ToPropertyKey (P). - Return ?
HasOwnProperty (obj, key).
20.1.2.15 Object.is ( value1, value2 )
This function performs the following steps when called:
- Return
SameValue (value1, value2).
20.1.2.16 Object.isExtensible ( O )
This function performs the following steps when called:
- If O
is not an Object , returnfalse . - Return ?
IsExtensible (O).
20.1.2.17 Object.isFrozen ( O )
This function performs the following steps when called:
- If O
is not an Object , returntrue . - Return ?
TestIntegrityLevel (O,frozen ).
20.1.2.18 Object.isSealed ( O )
This function performs the following steps when called:
- If O
is not an Object , returntrue . - Return ?
TestIntegrityLevel (O,sealed ).
20.1.2.19 Object.keys ( O )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let keyList be ?
EnumerableOwnProperties (obj,key ). - Return
CreateArrayFromList (keyList).
20.1.2.20 Object.preventExtensions ( O )
This function performs the following steps when called:
- If O
is not an Object , return O. - Let status be ? O.[[PreventExtensions]]().
- If status is
false , throw aTypeError exception. - Return O.
20.1.2.21 Object.prototype
The initial value of Object.prototype is the
This property has the attributes { [[Writable]]:
20.1.2.22 Object.seal ( O )
This function performs the following steps when called:
- If O
is not an Object , return O. - Let status be ?
SetIntegrityLevel (O,sealed ). - If status is
false , throw aTypeError exception. - Return O.
20.1.2.23 Object.setPrototypeOf ( O, proto )
This function performs the following steps when called:
- Set O to ?
RequireObjectCoercible (O). - If proto
is not an Object and proto is notnull , throw aTypeError exception. - If O
is not an Object , return O. - Let status be ? O.[[SetPrototypeOf]](proto).
- If status is
false , throw aTypeError exception. - Return O.
20.1.2.24 Object.values ( O )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let valueList be ?
EnumerableOwnProperties (obj,value ). - Return
CreateArrayFromList (valueList).
20.1.3 Properties of the Object Prototype Object
The Object prototype object:
- is %Object.prototype%.
- has an [[Extensible]] internal slot whose value is
true . - has the internal methods defined for
ordinary objects , except for the [[SetPrototypeOf]] method, which is as defined in10.4.7.1 . (Thus, it is animmutable prototype exotic object .) - has a [[Prototype]] internal slot whose value is
null .
20.1.3.1 Object.prototype.constructor
The initial value of Object.prototype.constructor is
20.1.3.2 Object.prototype.hasOwnProperty ( V )
This method performs the following steps when called:
- Let P be ?
ToPropertyKey (V). - Let O be ?
ToObject (this value). - Return ?
HasOwnProperty (O, P).
20.1.3.3 Object.prototype.isPrototypeOf ( V )
This method performs the following steps when called:
- If V
is not an Object , returnfalse . - Let O be ?
ToObject (this value). - Repeat,
- Set V to ? V.[[GetPrototypeOf]]().
- If V is
null , returnfalse . - If
SameValue (O, V) istrue , returntrue .
20.1.3.4 Object.prototype.propertyIsEnumerable ( V )
This method performs the following steps when called:
- Let P be ?
ToPropertyKey (V). - Let O be ?
ToObject (this value). - Let desc be ? O.[[GetOwnProperty]](P).
- If desc is
undefined , returnfalse . - Return desc.[[Enumerable]].
This method does not consider objects in the prototype chain.
20.1.3.5 Object.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
This method performs the following steps when called:
- Let O be the
this value. - Return ?
Invoke (O,"toString" ).
The optional parameters to this method are not used but are intended to correspond to the
parameter pattern used by ECMA-402 toLocaleString methods. Implementations that
do not include ECMA-402 support must not use those parameter positions for other purposes.
This method provides a generic toLocaleString implementation for objects
that have no locale-sensitive toString behaviour. Array,
Number, Date, and toLocaleString methods.
ECMA-402 intentionally does not provide an alternative to this default implementation.
20.1.3.6 Object.prototype.toString ( )
This method performs the following steps when called:
- If the
this value isundefined , return"[object Undefined]" . - If the
this value isnull , return"[object Null]" . - Let O be !
ToObject (this value). - Let isArray be ?
IsArray (O). - If isArray is
true , let builtinTag be"Array" . - Else if O has a [[ParameterMap]] internal slot,
let builtinTag be
"Arguments" . - Else if O has a [[Call]] internal method, let
builtinTag be
"Function" . - Else if O has an [[ErrorData]] internal slot,
let builtinTag be
"Error" . - Else if O has a [[BooleanData]] internal slot,
let builtinTag be
"Boolean" . - Else if O has a [[NumberData]] internal slot,
let builtinTag be
"Number" . - Else if O has a [[StringData]] internal slot,
let builtinTag be
"String" . - Else if O has a [[DateValue]] internal slot, let
builtinTag be
"Date" . - Else if O has a [[RegExpMatcher]] internal slot,
let builtinTag be
"RegExp" . - Else, let builtinTag be
"Object" . - Let tag be ?
Get (O,%Symbol.toStringTag% ). - If tag
is not a String , set tag to builtinTag. - Return the
string-concatenation of"[object " , tag, and"]" .
Historically, this method was occasionally used to access the String value of the
[[Class]] internal slot that was used in previous editions
of this specification as a nominal type tag for various built-in objects. The above
definition of toString preserves compatibility for legacy code that
uses toString as a test for those specific kinds of built-in objects.
It does not provide a reliable type testing mechanism for other kinds of built-in or
program defined objects. In addition, programs can use
20.1.3.7 Object.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ToObject (this value).
20.1.3.8 Object.prototype.__proto__
Object.prototype.__proto__ is an
20.1.3.8.1 get Object.prototype.__proto__
The value of the [[Get]] attribute is a built-in function that requires no arguments. It performs the following steps when called:
- Let O be ?
ToObject (this value). - Return ? O.[[GetPrototypeOf]]().
20.1.3.8.2 set Object.prototype.__proto__
The value of the [[Set]] attribute is a built-in function that takes an argument proto. It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If proto
is not an Object and proto is notnull , returnundefined . - If O
is not an Object , returnundefined . - Let status be ? O.[[SetPrototypeOf]](proto).
- If status is
false , throw aTypeError exception. - Return
undefined .
20.1.3.9 Legacy Object.prototype Accessor Methods
20.1.3.9.1 Object.prototype.__defineGetter__ ( P, getter )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - If
IsCallable (getter) isfalse , throw aTypeError exception. - Let desc be PropertyDescriptor { [[Get]]:
getter, [[Enumerable]]:
true , [[Configurable]]:true }. - Let key be ?
ToPropertyKey (P). - Perform ?
DefinePropertyOrThrow (O, key, desc). - Return
undefined .
20.1.3.9.2 Object.prototype.__defineSetter__ ( P, setter )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - If
IsCallable (setter) isfalse , throw aTypeError exception. - Let desc be PropertyDescriptor { [[Set]]:
setter, [[Enumerable]]:
true , [[Configurable]]:true }. - Let key be ?
ToPropertyKey (P). - Perform ?
DefinePropertyOrThrow (O, key, desc). - Return
undefined .
20.1.3.9.3 Object.prototype.__lookupGetter__ ( P )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let key be ?
ToPropertyKey (P). - Repeat,
- Let desc be ? O.[[GetOwnProperty]](key).
- If desc is not
undefined , then- If
IsAccessorDescriptor (desc) istrue , return desc.[[Get]]. - Return
undefined .
- If
- Set O to ? O.[[GetPrototypeOf]]().
- If O is
null , returnundefined .
20.1.3.9.4 Object.prototype.__lookupSetter__ ( P )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let key be ?
ToPropertyKey (P). - Repeat,
- Let desc be ? O.[[GetOwnProperty]](key).
- If desc is not
undefined , then- If
IsAccessorDescriptor (desc) istrue , return desc.[[Set]]. - Return
undefined .
- If
- Set O to ? O.[[GetPrototypeOf]]().
- If O is
null , returnundefined .
20.1.4 Properties of Object Instances
Object instances have no special properties beyond those inherited from the
20.2 Function Objects
20.2.1 The Function Constructor
The Function
- is %Function%.
- is the initial value of the
"Function" property of theglobal object . - creates and initializes a new
function object when called as a function rather than as aconstructor . Thus the function callFunction(…)is equivalent to the object creation expressionnew Function(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Function behaviour must include asupercall to the Functionconstructor to create and initialize a subclass instance with the internal slots necessary for built-in function behaviour. All ECMAScript syntactic forms for definingfunction objects create instances of Function. There is no syntactic means to create instances of Function subclasses except for the built-in GeneratorFunction, AsyncFunction, and AsyncGeneratorFunction subclasses.
20.2.1.1 Function ( ...parameterArgs, bodyArg )
The last argument (if any) specifies the body (executable code) of a function; any preceding arguments specify formal parameters.
This function performs the following steps when called:
- Let C be the
active function object . - If bodyArg is not present, set bodyArg to the empty String.
- Return ?
CreateDynamicFunction (C, NewTarget,normal , parameterArgs, bodyArg).
It is permissible but not necessary to have one argument for each formal parameter to be specified. For example, all three of the following expressions produce the same result:
new Function("a", "b", "c", "return a+b+c")
new Function("a, b, c", "return a+b+c")
new Function("a,b", "c", "return a+b+c")20.2.1.1.1 CreateDynamicFunction ( constructor, newTarget, kind, parameterArgs, bodyArg )
The abstract operation CreateDynamicFunction takes arguments constructor (a
new was initially applied to. parameterArgs and
bodyArg reflect the argument values that were passed to
constructor. It performs the following steps when called:
- If newTarget is
undefined , set newTarget to constructor. - If kind is
normal , then- Let prefix be
"function" . - Let exprSym be the grammar symbol
FunctionExpression . - Let bodySym be the grammar symbol
FunctionBody .[~Yield, ~Await] - Let parameterSym be the grammar symbol
FormalParameters .[~Yield, ~Await] - Let fallbackProto be
"%Function.prototype%" .
- Let prefix be
- Else if kind is
generator , then- Let prefix be
"function*" . - Let exprSym be the grammar symbol
GeneratorExpression . - Let bodySym be the grammar symbol
GeneratorBody . - Let parameterSym be the grammar symbol
FormalParameters .[+Yield, ~Await] - Let fallbackProto be
"%GeneratorFunction.prototype%" .
- Let prefix be
- Else if kind is
async , then- Let prefix be
"async function" . - Let exprSym be the grammar symbol
AsyncFunctionExpression . - Let bodySym be the grammar symbol
AsyncFunctionBody . - Let parameterSym be the grammar symbol
FormalParameters .[~Yield, +Await] - Let fallbackProto be
"%AsyncFunction.prototype%" .
- Let prefix be
- Else,
Assert : kind isasync-generator .- Let prefix be
"async function*" . - Let exprSym be the grammar symbol
AsyncGeneratorExpression . - Let bodySym be the grammar symbol
AsyncGeneratorBody . - Let parameterSym be the grammar symbol
FormalParameters .[+Yield, +Await] - Let fallbackProto be
"%AsyncGeneratorFunction.prototype%" .
- Let argCount be the number of elements in parameterArgs.
- Let parameterStrings be a new empty
List . - For each element arg of parameterArgs, do
- Append ?
ToString (arg) to parameterStrings.
- Append ?
- Let bodyString be ?
ToString (bodyArg). - Let currentRealm be
the current Realm Record . - Perform ?
HostEnsureCanCompileStrings (currentRealm, parameterStrings, bodyString,false ). - Let P be the empty String.
- If argCount > 0, then
- Set P to parameterStrings[0].
- Let k be 1.
- Repeat, while k < argCount,
- Let nextArgString be parameterStrings[k].
- Set P to the
string-concatenation of P,"," (a comma), and nextArgString. - Set k to k + 1.
- Let bodyParseString be the
string-concatenation of 0x000A (LINE FEED), bodyString, and 0x000A (LINE FEED). - Let sourceString be the
string-concatenation of prefix," anonymous(" , P, 0x000A (LINE FEED),") {" , bodyParseString, and"}" . - Let sourceText be
StringToCodePoints (sourceString). - Let parameters be
ParseText (P, parameterSym). - If parameters is a
List of errors, throw aSyntaxError exception. - Let body be
ParseText (bodyParseString, bodySym). - If body is a
List of errors, throw aSyntaxError exception. - NOTE: The parameters and body are parsed separately to ensure that each is valid
alone. For example,
new Function("/*", "*/ ) {")does not evaluate to a function. - NOTE: If this step is reached, sourceText must have the syntax of exprSym (although the reverse implication does not hold). The purpose of the next two steps is to enforce any Early Error rules which apply to exprSym directly.
- Let expr be
ParseText (sourceText, exprSym). - If expr is a
List of errors, throw aSyntaxError exception. - Let proto be ?
GetPrototypeFromConstructor (newTarget, fallbackProto). - Let env be currentRealm.[[GlobalEnv]].
- Let privateEnv be
null . - Let F be
OrdinaryFunctionCreate (proto, sourceText, parameters, body,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F,"anonymous" ). - If kind is
generator , then- Let prototype be
OrdinaryObjectCreate (%GeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }).
- Let prototype be
- Else if kind is
async-generator , then- Let prototype be
OrdinaryObjectCreate (%AsyncGeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }).
- Let prototype be
- Else if kind is
normal , then- Perform
MakeConstructor (F).
- Perform
- NOTE: Functions whose kind is
async are not constructable and do not have a [[Construct]] internal method or a"prototype" property. - Return F.
CreateDynamicFunction defines a
20.2.2 Properties of the Function Constructor
The Function
- is itself a built-in
function object . - has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"length" property whose value is1 𝔽. - has the following properties:
20.2.2.1 Function.prototype
The value of Function.prototype is the
This property has the attributes { [[Writable]]:
20.2.3 Properties of the Function Prototype Object
The Function prototype object:
- is %Function.prototype%.
- is itself a built-in
function object . - accepts any arguments and returns
undefined when invoked. - does not have a [[Construct]] internal method; it cannot be used as
a
constructor with thenewoperator. - has a [[Prototype]] internal slot whose value is
%Object.prototype% . - does not have a
"prototype" property. - has a
"length" property whose value is+0 𝔽. - has a
"name" property whose value is the empty String.
The Function prototype object is specified to be a
20.2.3.1 Function.prototype.apply ( thisArg, argArray )
This method performs the following steps when called:
- Let func be the
this value. - If
IsCallable (func) isfalse , throw aTypeError exception. - If argArray is either
undefined ornull , then- Perform
PrepareForTailCall (). - Return ?
Call (func, thisArg).
- Perform
- Let argList be ?
CreateListFromArrayLike (argArray). - Perform
PrepareForTailCall (). - Return ?
Call (func, thisArg, argList).
The thisArg value is passed without modification as the
If func is either an arrow function or a
20.2.3.2 Function.prototype.bind ( thisArg, ...args )
This method performs the following steps when called:
- Let Target be the
this value. - If
IsCallable (Target) isfalse , throw aTypeError exception. - Let F be ?
BoundFunctionCreate (Target, thisArg, args). - Let L be 0.
- Let targetHasLength be ?
HasOwnProperty (Target,"length" ). - If targetHasLength is
true , then- Let targetLen be ?
Get (Target,"length" ). - If targetLen
is a Number , then- If targetLen is
+∞ 𝔽, then- Set L to +∞.
- Else if targetLen is
-∞ 𝔽, then- Set L to 0.
- Else,
- Let targetLenAsInt be !
ToIntegerOrInfinity (targetLen). Assert : targetLenAsInt isfinite .- Let argCount be the number of elements in args.
- Set L to
max (targetLenAsInt - argCount, 0).
- Let targetLenAsInt be !
- If targetLen is
- Let targetLen be ?
- Perform
SetFunctionLength (F, L). - Let targetName be ?
Get (Target,"name" ). - If targetName
is not a String , set targetName to the empty String. - Perform
SetFunctionName (F, targetName,"bound" ). - Return F.
Function.prototype.bind
are
If Target is either an arrow function or a
20.2.3.3 Function.prototype.call ( thisArg, ...args )
This method performs the following steps when called:
- Let func be the
this value. - If
IsCallable (func) isfalse , throw aTypeError exception. - Perform
PrepareForTailCall (). - Return ?
Call (func, thisArg, args).
The thisArg value is passed without modification as the
If func is either an arrow function or a
20.2.3.4 Function.prototype.constructor
The initial value of Function.prototype.constructor is
20.2.3.5 Function.prototype.toString ( )
This method performs the following steps when called:
- Let func be the
this value. - If func
is an Object , func has a [[SourceText]] internal slot, func.[[SourceText]] is a sequence of Unicode code points, andHostHasSourceTextAvailable (func) istrue , then- Return
CodePointsToString (func.[[SourceText]]).
- Return
- If func is a
built-in function object , return animplementation-defined String source code representation of func. The representation must have the syntax of aNativeFunction . Additionally, if func has an [[InitialName]] internal slot and func.[[InitialName]]is a String , the portion of the returned String that would be matched byNativeFunctionAccessor opt PropertyName must be func.[[InitialName]]. - If func
is an Object andIsCallable (func) istrue , return animplementation-defined String source code representation of func. The representation must have the syntax of aNativeFunction . - Throw a
TypeError exception.
20.2.3.6 Function.prototype [ %Symbol.hasInstance% ] ( V )
This method performs the following steps when called:
- Let F be the
this value. - Return ?
OrdinaryHasInstance (F, V).
This property has the attributes { [[Writable]]:
This is the default implementation of %Symbol.hasInstance% that most
functions inherit. %Symbol.hasInstance% is called by the
instanceof operator to determine whether a value is an instance of a
specific
v instanceof Fevaluates as
F[%Symbol.hasInstance%](v)A instanceof by exposing a
different %Symbol.hasInstance% method on the function.
This property is non-writable and non-configurable to prevent tampering that could be used to globally expose the target function of a bound function.
The value of the
20.2.4 Function Instances
Every Function instance is an ECMAScript Function.prototype.bind method
(
Function instances have the following properties:
20.2.4.1 length
The value of the
20.2.4.2 name
The value of the
Anonymous functions objects that do not have a contextual name associated with them by this
specification use the empty String as the value of the
20.2.4.3 prototype
Function instances that can be used as a
This property has the attributes { [[Writable]]:
Function.prototype.bind,
or by evaluating a
20.2.5 HostHasSourceTextAvailable ( func )
The
An implementation of HostHasSourceTextAvailable must conform to the following requirements:
- It must be deterministic with respect to its parameters. Each time it is called with a specific func as its argument, it must return the same result.
The default implementation of HostHasSourceTextAvailable is to return
20.3 Boolean Objects
20.3.1 The Boolean Constructor
The Boolean
- is %Boolean%.
- is the initial value of the
"Boolean" property of theglobal object . - creates and initializes a new Boolean object when called as a
constructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Boolean behaviour must include asupercall to the Booleanconstructor to create and initialize the subclass instance with a [[BooleanData]] internal slot.
20.3.1.1 Boolean ( value )
This function performs the following steps when called:
- Let b be
ToBoolean (value). - If NewTarget is
undefined , return b. - Let O be ?
OrdinaryCreateFromConstructor (NewTarget,"%Boolean.prototype%" , « [[BooleanData]] »). - Set O.[[BooleanData]] to b.
- Return O.
20.3.2 Properties of the Boolean Constructor
The Boolean
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
20.3.2.1 Boolean.prototype
The initial value of Boolean.prototype is the
This property has the attributes { [[Writable]]:
20.3.3 Properties of the Boolean Prototype Object
The Boolean prototype object:
- is %Boolean.prototype%.
- is an
ordinary object . - is itself a Boolean object; it has a [[BooleanData]] internal slot
with the value
false . - has a [[Prototype]] internal slot whose value is
%Object.prototype% .
20.3.3.1 Boolean.prototype.constructor
The initial value of Boolean.prototype.constructor is
20.3.3.2 Boolean.prototype.toString ( )
This method performs the following steps when called:
- Let b be ?
ThisBooleanValue (this value). - If b is
true , return"true" ; else return"false" .
20.3.3.3 Boolean.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ThisBooleanValue (this value).
20.3.3.3.1 ThisBooleanValue ( value )
The abstract operation ThisBooleanValue takes argument value (an
- If value
is a Boolean , return value. - If value
is an Object and value has a [[BooleanData]] internal slot, then- Let b be value.[[BooleanData]].
Assert : bis a Boolean .- Return b.
- Throw a
TypeError exception.
20.3.4 Properties of Boolean Instances
Boolean instances are
20.4 Symbol Objects
20.4.1 The Symbol Constructor
The Symbol
- is %Symbol%.
- is the initial value of the
"Symbol" property of theglobal object . - returns a new Symbol value when called as a function.
- is not intended to be used with the
newoperator. - is not intended to be subclassed.
- may be used as the value of an
extendsclause of a class definition but asupercall to it will cause an exception.
20.4.1.1 Symbol ( [ description ] )
This function performs the following steps when called:
- If NewTarget is not
undefined , throw aTypeError exception. - If description is
undefined , let descString beundefined . - Else, let descString be ?
ToString (description). - Return a new Symbol whose [[Description]] is descString.
20.4.2 Properties of the Symbol Constructor
The Symbol
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
20.4.2.1 Symbol.asyncIterator
The initial value of Symbol.asyncIterator is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.2 Symbol.for ( key )
This function performs the following steps when called:
- Let stringKey be ?
ToString (key). - For each element e of the
GlobalSymbolRegistry List , do- If e.[[Key]] is stringKey, return e.[[Symbol]].
Assert : TheGlobalSymbolRegistry List does not currently contain an entry for stringKey.- Let newSymbol be a new Symbol whose [[Description]] is stringKey.
- Append the GlobalSymbolRegistry
Record { [[Key]]: stringKey, [[Symbol]]: newSymbol } to theGlobalSymbolRegistry List . - Return newSymbol.
The GlobalSymbolRegistry List is an append-only
20.4.2.3 Symbol.hasInstance
The initial value of Symbol.hasInstance is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.4 Symbol.isConcatSpreadable
The initial value of Symbol.isConcatSpreadable is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.5 Symbol.iterator
The initial value of Symbol.iterator is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.6 Symbol.keyFor ( sym )
This function performs the following steps when called:
- If sym
is not a Symbol , throw aTypeError exception. - Return
KeyForSymbol (sym).
20.4.2.7 Symbol.match
The initial value of Symbol.match is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.8 Symbol.matchAll
The initial value of Symbol.matchAll is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.9 Symbol.prototype
The initial value of Symbol.prototype is the
This property has the attributes { [[Writable]]:
20.4.2.10 Symbol.replace
The initial value of Symbol.replace is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.11 Symbol.search
The initial value of Symbol.search is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.12 Symbol.species
The initial value of Symbol.species is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.13 Symbol.split
The initial value of Symbol.split is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.14 Symbol.toPrimitive
The initial value of Symbol.toPrimitive is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.15 Symbol.toStringTag
The initial value of Symbol.toStringTag is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.16 Symbol.unscopables
The initial value of Symbol.unscopables is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.3 Properties of the Symbol Prototype Object
The Symbol prototype object:
- is %Symbol.prototype%.
- is an
ordinary object . is not a Symbol instance and does not have a [[SymbolData]] internal slot.- has a [[Prototype]] internal slot whose value is
%Object.prototype% .
20.4.3.1 Symbol.prototype.constructor
The initial value of Symbol.prototype.constructor is
20.4.3.2 get Symbol.prototype.description
Symbol.prototype.description is an
- Let s be the
this value. - Let sym be ?
ThisSymbolValue (s). - Return sym.[[Description]].
20.4.3.3 Symbol.prototype.toString ( )
This method performs the following steps when called:
- Let sym be ?
ThisSymbolValue (this value). - Return
SymbolDescriptiveString (sym).
20.4.3.3.1 SymbolDescriptiveString ( sym )
The abstract operation SymbolDescriptiveString takes argument sym (a Symbol) and returns a String. It performs the following steps when called:
- Let desc be sym's [[Description]] value.
- If desc is
undefined , set desc to the empty String. Assert : descis a String .- Return the
string-concatenation of"Symbol(" , desc, and")" .
20.4.3.4 Symbol.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ThisSymbolValue (this value).
20.4.3.4.1 ThisSymbolValue ( value )
The abstract operation ThisSymbolValue takes argument value (an
- If value
is a Symbol , return value. - If value
is an Object and value has a [[SymbolData]] internal slot, then- Let s be value.[[SymbolData]].
Assert : sis a Symbol .- Return s.
- Throw a
TypeError exception.
20.4.3.5 Symbol.prototype [ %Symbol.toPrimitive% ] ( hint )
This method is called by ECMAScript language operators to convert a Symbol object to a primitive value.
It performs the following steps when called:
- Return ?
ThisSymbolValue (this value).
The argument is ignored.
This property has the attributes { [[Writable]]:
The value of the
20.4.3.6 Symbol.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
20.4.4 Properties of Symbol Instances
Symbol instances are
20.4.5 Abstract Operations for Symbols
20.4.5.1 KeyForSymbol ( sym )
The abstract operation KeyForSymbol takes argument sym (a Symbol) and returns a
String or
- For each element e of the
GlobalSymbolRegistry List , do- If
SameValue (e.[[Symbol]], sym) istrue , return e.[[Key]].
- If
Assert : TheGlobalSymbolRegistry List does not currently contain an entry for sym.- Return
undefined .
20.5 Error Objects
Instances of Error objects are thrown as exceptions when runtime errors occur. The Error objects may also serve as base objects for user-defined exception classes.
When an ECMAScript implementation detects a runtime error, it throws a new instance of one of the
NativeError objects defined in
20.5.1 The Error Constructor
The Error
- is %Error%.
- is the initial value of the
"Error" property of theglobal object . - creates and initializes a new Error object when called as a function rather than as a
constructor . Thus the function callError(…)is equivalent to the object creation expressionnew Error(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Error behaviour must include asupercall to the Errorconstructor to create and initialize subclass instances with an [[ErrorData]] internal slot.
20.5.1.1 Error ( message [ , options ] )
This function performs the following steps when called:
- If NewTarget is
undefined , let newTarget be theactive function object ; else let newTarget be NewTarget. - Let O be ?
OrdinaryCreateFromConstructor (newTarget,"%Error.prototype%" , « [[ErrorData]] »). - If message is not
undefined , then- Let msg be ?
ToString (message). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"message" , msg).
- Let msg be ?
- Perform ?
InstallErrorCause (O, options). - Return O.
20.5.2 Properties of the Error Constructor
The Error
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
20.5.2.1 Error.isError ( arg )
This function performs the following steps when called:
- If arg
is not an Object , returnfalse . - If arg does not have an [[ErrorData]] internal
slot, return
false . - Return
true .
20.5.2.2 Error.prototype
The initial value of Error.prototype is the
This property has the attributes { [[Writable]]:
20.5.3 Properties of the Error Prototype Object
The Error prototype object:
- is %Error.prototype%.
- is an
ordinary object . - is not an Error instance and does not have an [[ErrorData]] internal slot.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% .
20.5.3.1 Error.prototype.constructor
The initial value of Error.prototype.constructor is
20.5.3.2 Error.prototype.message
The initial value of Error.prototype.message is the empty String.
20.5.3.3 Error.prototype.name
The initial value of Error.prototype.name is
20.5.3.4 Error.prototype.toString ( )
This method performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - Let name be ?
Get (O,"name" ). - If name is
undefined , set name to"Error" ; otherwise set name to ?ToString (name). - Let msg be ?
Get (O,"message" ). - If msg is
undefined , set msg to the empty String; otherwise set msg to ?ToString (msg). - If name is the empty String, return msg.
- If msg is the empty String, return name.
- Return the
string-concatenation of name, the code unit 0x003A (COLON), the code unit 0x0020 (SPACE), and msg.
20.5.4 Properties of Error Instances
Error instances are Object.prototype.toString
and Error.isError.
20.5.5 Native Error Types Used in This Standard
A new instance of one of the NativeError objects below or of the AggregateError object
is thrown when a runtime error is detected. All NativeError objects share the same
structure, as described in
20.5.5.1 EvalError
The EvalError
This exception is not currently used within this specification. This object remains for compatibility with previous editions of this specification.
20.5.5.2 RangeError
The RangeError
Indicates a value that is not in the set or range of allowable values.
20.5.5.3 ReferenceError
The ReferenceError
Indicate that an invalid reference has been detected.
20.5.5.4 SyntaxError
The SyntaxError
Indicates that a parsing error has occurred.
20.5.5.5 TypeError
The TypeError
TypeError is used to indicate an unsuccessful operation when none of the other NativeError objects are an appropriate indication of the failure cause.
20.5.5.6 URIError
The URIError
Indicates that one of the global URI handling functions was used in a way that is incompatible with its definition.
20.5.6 NativeError Object Structure
Each of these objects has the structure described below, differing only in the name used as the
For each error object, references to NativeError in the definition should be replaced
with the appropriate error object name from
20.5.6.1 The NativeError Constructors
Each NativeError
- creates and initializes a new NativeError object when called as a function
rather than as a
constructor . A call of the object as a function is equivalent to calling it as aconstructor with the same arguments. Thus the function callNativeError(…)is equivalent to the object creation expressionnew NativeError(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified NativeError behaviour must include asupercall to the NativeErrorconstructor to create and initialize subclass instances with an [[ErrorData]] internal slot.
20.5.6.1.1 NativeError ( message [ , options ] )
Each NativeError function performs the following steps when called:
- If NewTarget is
undefined , let newTarget be theactive function object ; else let newTarget be NewTarget. - Let O be
?
OrdinaryCreateFromConstructor (newTarget,"%NativeError.prototype%", « [[ErrorData]] »). - If message is not
undefined , then- Let msg be ?
ToString (message). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"message" , msg).
- Let msg be ?
- Perform ?
InstallErrorCause (O, options). - Return O.
The actual value of the string passed in step
20.5.6.2 Properties of the NativeError Constructors
Each NativeError
- has a [[Prototype]] internal slot whose value is
%Error% . - has a
"name" property whose value is the String value"NativeError" . - has the following properties:
20.5.6.2.1 NativeError.prototype
The initial value of NativeError.prototype is a
NativeError prototype object (
This property has the attributes { [[Writable]]:
20.5.6.3 Properties of the NativeError Prototype Objects
Each NativeError prototype object:
- is an
ordinary object . - is not an Error instance and does not have an [[ErrorData]] internal slot.
- has a [[Prototype]] internal slot whose value is
%Error.prototype% .
20.5.6.3.1 NativeError.prototype.constructor
The initial value of the
20.5.6.3.2 NativeError.prototype.message
The initial value of the
20.5.6.3.3 NativeError.prototype.name
The initial value of the
20.5.6.4 Properties of NativeError Instances
NativeError instances are Object.prototype.toString
(Error.isError (
20.5.7 AggregateError Objects
20.5.7.1 The AggregateError Constructor
The AggregateError
- is %AggregateError%.
- is the initial value of the
"AggregateError" property of theglobal object . - creates and initializes a new AggregateError object when called as a function rather
than as a
constructor . Thus the function callAggregateError(…)is equivalent to the object creation expressionnew AggregateError(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified AggregateError behaviour must include asupercall to the AggregateErrorconstructor to create and initialize subclass instances with an [[ErrorData]] internal slot.
20.5.7.1.1 AggregateError ( errors, message [ , options ] )
This function performs the following steps when called:
- If NewTarget is
undefined , let newTarget be theactive function object ; else let newTarget be NewTarget. - Let O be ?
OrdinaryCreateFromConstructor (newTarget,"%AggregateError.prototype%" , « [[ErrorData]] »). - If message is not
undefined , then- Let msg be ?
ToString (message). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"message" , msg).
- Let msg be ?
- Perform ?
InstallErrorCause (O, options). - Let errorsList be ?
IteratorToList (?GetIterator (errors,sync )). - Perform !
DefinePropertyOrThrow (O,"errors" , PropertyDescriptor { [[Configurable]]:true , [[Enumerable]]:false , [[Writable]]:true , [[Value]]:CreateArrayFromList (errorsList) }). - Return O.
20.5.7.2 Properties of the AggregateError Constructor
The AggregateError
- has a [[Prototype]] internal slot whose value is
%Error% . - has the following properties:
20.5.7.2.1 AggregateError.prototype
The initial value of AggregateError.prototype is
This property has the attributes { [[Writable]]:
20.5.7.3 Properties of the AggregateError Prototype Object
The AggregateError prototype object:
- is %AggregateError.prototype%.
- is an
ordinary object . - is not an Error instance or an AggregateError instance and does not have an [[ErrorData]] internal slot.
- has a [[Prototype]] internal slot whose value is
%Error.prototype% .
20.5.7.3.1 AggregateError.prototype.constructor
The initial value of AggregateError.prototype.constructor is
20.5.7.3.2 AggregateError.prototype.message
The initial value of AggregateError.prototype.message is the empty String.
20.5.7.3.3 AggregateError.prototype.name
The initial value of AggregateError.prototype.name is
20.5.7.4 Properties of AggregateError Instances
AggregateError instances are Object.prototype.toString
(Error.isError (
20.5.8 Abstract Operations for Error Objects
20.5.8.1 InstallErrorCause ( O, options )
The abstract operation InstallErrorCause takes arguments O (an Object) and
options (an
- If options
is an Object and ?HasProperty (options,"cause" ) istrue , then- Let cause be ?
Get (options,"cause" ). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"cause" , cause).
- Let cause be ?
- Return
unused .
21 Numbers and Dates
21.1 Number Objects
21.1.1 The Number Constructor
The Number
- is %Number%.
- is the initial value of the
"Number" property of theglobal object . - creates and initializes a new Number object when called as a
constructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Number behaviour must include asupercall to the Numberconstructor to create and initialize the subclass instance with a [[NumberData]] internal slot.
21.1.1.1 Number ( value )
This function performs the following steps when called:
- If value is present, then
- Let prim be ?
ToNumeric (value). - If prim
is a BigInt , let n be𝔽 (ℝ (prim)). - Otherwise, let n be prim.
- Let prim be ?
- Else,
- Let n be
+0 𝔽.
- Let n be
- If NewTarget is
undefined , return n. - Let O be ?
OrdinaryCreateFromConstructor (NewTarget,"%Number.prototype%" , « [[NumberData]] »). - Set O.[[NumberData]] to n.
- Return O.
21.1.2 Properties of the Number Constructor
The Number
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
21.1.2.1 Number.EPSILON
The value of Number.EPSILON is the
This property has the attributes { [[Writable]]:
21.1.2.2 Number.isFinite ( number )
This function performs the following steps when called:
- If number
is not a Number , returnfalse . - If number is not
finite , returnfalse . - Otherwise, return
true .
21.1.2.3 Number.isInteger ( number )
This function performs the following steps when called:
- If number is an
integral Number , returntrue . - Return
false .
21.1.2.4 Number.isNaN ( number )
This function performs the following steps when called:
- If number
is not a Number , returnfalse . - If number is
NaN , returntrue . - Otherwise, return
false .
This function differs from the global isNaN function (
21.1.2.5 Number.isSafeInteger ( number )
An
This function performs the following steps when called:
- If number is an
integral Number , then - Return
false .
21.1.2.6 Number.MAX_SAFE_INTEGER
Due to rounding behaviour necessitated by precision limitations of Number.MAX_SAFE_INTEGER is shared with at least one other
9007199254740992 and
9007199254740993 evaluate to the Number value
The value of Number.MAX_SAFE_INTEGER is
This property has the attributes { [[Writable]]:
21.1.2.7 Number.MAX_VALUE
The value of Number.MAX_VALUE is the largest positive
This property has the attributes { [[Writable]]:
21.1.2.8 Number.MIN_SAFE_INTEGER
Due to rounding behaviour necessitated by precision limitations of Number.MIN_SAFE_INTEGER is shared with at least one other
-9007199254740992
and -9007199254740993 evaluate to the Number value
The value of Number.MIN_SAFE_INTEGER is
This property has the attributes { [[Writable]]:
21.1.2.9 Number.MIN_VALUE
The value of Number.MIN_VALUE is the smallest positive value of the
In the Number.MIN_VALUE must be the smallest non-zero positive
value that can actually be represented by the implementation.
This property has the attributes { [[Writable]]:
21.1.2.10 Number.NaN
The value of Number.NaN is
This property has the attributes { [[Writable]]:
21.1.2.11 Number.NEGATIVE_INFINITY
The value of Number.NEGATIVE_INFINITY is
This property has the attributes { [[Writable]]:
21.1.2.12 Number.parseFloat ( string )
The initial value of the
21.1.2.13 Number.parseInt ( string, radix )
The initial value of the
21.1.2.14 Number.POSITIVE_INFINITY
The value of Number.POSITIVE_INFINITY is
This property has the attributes { [[Writable]]:
21.1.2.15 Number.prototype
The initial value of Number.prototype is the
This property has the attributes { [[Writable]]:
21.1.3 Properties of the Number Prototype Object
The Number prototype object:
- is %Number.prototype%.
- is an
ordinary object . - is itself a Number object; it has a [[NumberData]] internal slot
with the value
+0 𝔽. - has a [[Prototype]] internal slot whose value is
%Object.prototype% .
Unless explicitly stated otherwise, the methods of the Number prototype object defined below are
not generic and the
The phrase “this Number value” within the specification of a method refers to the result returned
by calling the abstract operation
21.1.3.1 Number.prototype.constructor
The initial value of Number.prototype.constructor is
21.1.3.2 Number.prototype.toExponential ( fractionDigits )
This method returns a String containing this Number value represented in decimal exponential
notation with one digit before the significand's decimal point and fractionDigits
digits after the significand's decimal point. If fractionDigits is
It performs the following steps when called:
- Let x be ?
ThisNumberValue (this value). - Let f be ?
ToIntegerOrInfinity (fractionDigits). Assert : If fractionDigits isundefined , then f is 0.- If x is not
finite , returnNumber::toString (x, 10). - If f < 0 or f > 100, throw a
RangeError exception. - Set x to
ℝ (x). - Let s be the empty String.
- If x < 0, then
- Set s to
"-" . - Set x to -x.
- Set s to
- If x = 0, then
- Let m be the String value consisting of f + 1 occurrences of the code unit 0x0030 (DIGIT ZERO).
- Let e be 0.
- Else,
- If fractionDigits is not
undefined , then- Let e and n be
integers such that 10f ≤ n < 10f + 1 and for which n × 10e - f - x is as close to zero as possible. If there are two such sets of e and n, pick the e and n for which n × 10e - f is larger.
- Let e and n be
- Else,
- Let
e, n, and ff be
integers such that ff ≥ 0, 10ff ≤ n < 10ff + 1,𝔽 (n × 10e - ff) is𝔽 (x), and ff is as small as possible. Note that the decimal representation of n has ff + 1 digits, n is not divisible by 10, and the least significant digit of n is not necessarily uniquely determined by these criteria. - Set f to ff.
- Let
e, n, and ff be
- Let m be the String value consisting of the digits of the decimal representation of n (in order, with no leading zeroes).
- If fractionDigits is not
- If f ≠ 0, then
- Let a be the first code unit of m.
- Let b be the other f code units of m.
- Set m to the
string-concatenation of a,"." , and b.
- If e = 0, then
- Let c be
"+" . - Let d be
"0" .
- Let c be
- Else,
- If e > 0, then
- Let c be
"+" .
- Let c be
- Else,
Assert : e < 0.- Let c be
"-" . - Set e to -e.
- Let d be the String value consisting of the digits of the decimal representation of e (in order, with no leading zeroes).
- If e > 0, then
- Set m to the
string-concatenation of m,"e" , c, and d. - Return the
string-concatenation of s and m.
For implementations that provide more accurate conversions than required by the rules
above, it is recommended that the following alternative version of step
- Let e, n, and f be
integers such that f ≥ 0, 10f ≤ n < 10f + 1,𝔽 (n × 10e - f) is𝔽 (x), and f is as small as possible. If there are multiple possibilities for n, choose the value of n for which𝔽 (n × 10e - f) is closest in value to𝔽 (x). If there are two such possible values of n, choose the one that is even.
21.1.3.3 Number.prototype.toFixed ( fractionDigits )
This method returns a String containing this Number value represented in decimal
fixed-point notation with fractionDigits digits after the decimal point.
If fractionDigits is
It performs the following steps when called:
- Let x be ?
ThisNumberValue (this value). - Let f be ?
ToIntegerOrInfinity (fractionDigits). Assert : If fractionDigits isundefined , then f is 0.- If f is not
finite , throw aRangeError exception. - If f < 0 or f > 100, throw a
RangeError exception. - If x is not
finite , returnNumber::toString (x, 10). - Set x to
ℝ (x). - Let s be the empty String.
- If x < 0, then
- Set s to
"-" . - Set x to -x.
- Set s to
- If x ≥ 1021, then
- Else,
- Let n be an
integer for which n / 10f - x is as close to zero as possible. If there are two such n, pick the larger n. - If n = 0, let m be
"0" ; otherwise let m be the String value consisting of the digits of the decimal representation of n (in order, with no leading zeroes). - If f ≠ 0, then
- Let k be the length of m.
- If k ≤ f, then
- Let z be the String value consisting of f + 1 - k occurrences of the code unit 0x0030 (DIGIT ZERO).
- Set m to the
string-concatenation of z and m. - Set k to f + 1.
- Let a be the first k - f code units of m.
- Let b be the other f code units of m.
- Set m to the
string-concatenation of a,"." , and b.
- Let n be an
- Return the
string-concatenation of s and m.
The output of toFixed may be more precise than toString for
some values because toString only prints enough significant digits to distinguish
the number from adjacent Number values. For example,
(1000000000000000128).toString() returns
(1000000000000000128).toFixed(0) returns
21.1.3.4 Number.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method produces a String value that represents this Number value formatted according to
the conventions of the toString.
The meanings of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.1.3.5 Number.prototype.toPrecision ( precision )
This method returns a String containing this Number value represented either in decimal
exponential notation with one digit before the significand's decimal point and
It performs the following steps when called:
- Let x be ?
ThisNumberValue (this value). - If precision is
undefined , return !ToString (x). - Let p be ?
ToIntegerOrInfinity (precision). - If x is not
finite , returnNumber::toString (x, 10). - If p < 1 or p > 100, throw a
RangeError exception. - Set x to
ℝ (x). - Let s be the empty String.
- If x < 0, then
- Set s to the code unit 0x002D (HYPHEN-MINUS).
- Set x to -x.
- If x = 0, then
- Let m be the String value consisting of p occurrences of the code unit 0x0030 (DIGIT ZERO).
- Let e be 0.
- Else,
- Let e and n be
integers such that 10p - 1 ≤ n < 10p and for which n × 10e - p + 1 - x is as close to zero as possible. If there are two such sets of e and n, pick the e and n for which n × 10e - p + 1 is larger. - Let m be the String value consisting of the digits of the decimal representation of n (in order, with no leading zeroes).
- If e < -6 or e ≥ p, then
Assert : e ≠ 0.- If p ≠ 1, then
- Let a be the first code unit of m.
- Let b be the other p - 1 code units of m.
- Set m to the
string-concatenation of a,"." , and b.
- If e > 0, then
- Let c be the code unit 0x002B (PLUS SIGN).
- Else,
Assert : e < 0.- Let c be the code unit 0x002D (HYPHEN-MINUS).
- Set e to -e.
- Let d be the String value consisting of the digits of the decimal representation of e (in order, with no leading zeroes).
- Return the
string-concatenation of s, m, the code unit 0x0065 (LATIN SMALL LETTER E), c, and d.
- Let e and n be
- If e = p - 1, return the
string-concatenation of s and m. - If e ≥ 0, then
- Set m to the
string-concatenation of the first e + 1 code units of m, the code unit 0x002E (FULL STOP), and the remaining p - (e + 1) code units of m.
- Set m to the
- Else,
- Set m to the
string-concatenation of the code unit 0x0030 (DIGIT ZERO), the code unit 0x002E (FULL STOP), -(e + 1) occurrences of the code unit 0x0030 (DIGIT ZERO), and the String m.
- Set m to the
- Return the
string-concatenation of s and m.
21.1.3.6 Number.prototype.toString ( [ radix ] )
The optional radix should be an
This method performs the following steps when called:
- Let x be ?
ThisNumberValue (this value). - If radix is
undefined , let radixMV be 10. - Else, let radixMV be ?
ToIntegerOrInfinity (radix). - If radixMV is not in the
inclusive interval from 2 to 36, throw aRangeError exception. - Return
Number::toString (x, radixMV).
This method is not generic; it throws a
The
21.1.3.7 Number.prototype.valueOf ( )
- Return ?
ThisNumberValue (this value).
21.1.3.7.1 ThisNumberValue ( value )
The abstract operation ThisNumberValue takes argument value (an
- If value
is a Number , return value. - If value
is an Object and value has a [[NumberData]] internal slot, then- Let n be value.[[NumberData]].
Assert : nis a Number .- Return n.
- Throw a
TypeError exception.
21.1.4 Properties of Number Instances
Number instances are
21.2 BigInt Objects
21.2.1 The BigInt Constructor
The BigInt
- is %BigInt%.
- is the initial value of the
"BigInt" property of theglobal object . - performs a type conversion when called as a function rather than as a
constructor . - is not intended to be used with the
newoperator or to be subclassed. It may be used as the value of anextendsclause of a class definition but asupercall to the BigIntconstructor will cause an exception.
21.2.1.1 BigInt ( value )
This function performs the following steps when called:
- If NewTarget is not
undefined , throw aTypeError exception. - Let prim be ?
ToPrimitive (value,number ). - If prim
is a Number , return ?NumberToBigInt (prim). - Otherwise, return ?
ToBigInt (prim).
21.2.1.1.1 NumberToBigInt ( number )
The abstract operation NumberToBigInt takes argument number (a Number) and
returns either a
- If number is not an
integral Number , throw aRangeError exception. - Return
ℤ (ℝ (number)).
21.2.2 Properties of the BigInt Constructor
The BigInt
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
21.2.2.1 BigInt.asIntN ( bits, bigint )
This function performs the following steps when called:
21.2.2.2 BigInt.asUintN ( bits, bigint )
This function performs the following steps when called:
21.2.2.3 BigInt.prototype
The initial value of BigInt.prototype is the
This property has the attributes { [[Writable]]:
21.2.3 Properties of the BigInt Prototype Object
The BigInt prototype object:
- is %BigInt.prototype%.
- is an
ordinary object . is not a BigInt object; it does not have a [[BigIntData]] internal slot.- has a [[Prototype]] internal slot whose value is
%Object.prototype% .
The phrase “this BigInt value” within the specification of a method refers to the result returned
by calling the abstract operation
21.2.3.1 BigInt.prototype.constructor
The initial value of BigInt.prototype.constructor is
21.2.3.2 BigInt.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method produces a String value that represents this BigInt value formatted according to
the conventions of the toString.
The meanings of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.2.3.3 BigInt.prototype.toString ( [ radix ] )
The optional radix should be an
This method performs the following steps when called:
- Let x be ?
ThisBigIntValue (this value). - If radix is
undefined , let radixMV be 10. - Else, let radixMV be ?
ToIntegerOrInfinity (radix). - If radixMV is not in the
inclusive interval from 2 to 36, throw aRangeError exception. - Return
BigInt::toString (x, radixMV).
This method is not generic; it throws a
21.2.3.4 BigInt.prototype.valueOf ( )
- Return ?
ThisBigIntValue (this value).
21.2.3.4.1 ThisBigIntValue ( value )
The abstract operation ThisBigIntValue takes argument value (an
- If value
is a BigInt , return value. - If value
is an Object and value has a [[BigIntData]] internal slot, thenAssert : value.[[BigIntData]]is a BigInt .- Return value.[[BigIntData]].
- Throw a
TypeError exception.
21.2.3.5 BigInt.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
21.2.4 Properties of BigInt Instances
BigInt instances are
21.3 The Math Object
The Math object:
- is %Math%.
- is the initial value of the
"Math" property of theglobal object . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is not a
function object . - does not have a [[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a [[Call]] internal method; it cannot be invoked as a function.
In this specification, the phrase “the
21.3.1 Value Properties of the Math Object
21.3.1.1 Math.E
The
This property has the attributes { [[Writable]]:
21.3.1.2 Math.LN10
The
This property has the attributes { [[Writable]]:
21.3.1.3 Math.LN2
The
This property has the attributes { [[Writable]]:
21.3.1.4 Math.LOG10E
The
This property has the attributes { [[Writable]]:
The value of Math.LOG10E is approximately the reciprocal of the value of
Math.LN10.
21.3.1.5 Math.LOG2E
The
This property has the attributes { [[Writable]]:
The value of Math.LOG2E is approximately the reciprocal of the value of
Math.LN2.
21.3.1.6 Math.PI
The
This property has the attributes { [[Writable]]:
21.3.1.7 Math.SQRT1_2
The
This property has the attributes { [[Writable]]:
The value of Math.SQRT1_2 is approximately the reciprocal of the value
of Math.SQRT2.
21.3.1.8 Math.SQRT2
The
This property has the attributes { [[Writable]]:
21.3.1.9 Math [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
21.3.2 Function Properties of the Math Object
The behaviour of the functions acos, acosh, asin,
asinh, atan, atanh, atan2,
cbrt, cos, cosh, exp,
expm1, hypot, log, log1p,
log2, log10, pow, random,
sin, sinh, tan, and tanh is not
precisely specified here except to require specific results for certain argument values
that represent boundary cases of interest. For other argument values, these functions
are intended to compute approximations to the results of familiar mathematical
functions, but some latitude is allowed in the choice of approximation algorithms. The
general intent is that an implementer should be able to use the same mathematical
library for ECMAScript on a given hardware platform that is available to C programmers
on that platform.
Although the choice of algorithms is left to the implementation, it is recommended (but
not specified by this standard) that implementations use the approximation algorithms
for fdlibm, the freely
distributable mathematical library from Sun Microsystems (http://www.netlib.org/fdlibm).
21.3.2.1 Math.abs ( x )
This function returns the absolute value of x; the result has the same magnitude as x but has positive sign.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is
NaN , returnNaN . - If n is
-0 𝔽, return+0 𝔽. - If n is
-∞ 𝔽, return+∞ 𝔽. - If n <
-0 𝔽, return -n. - Return n.
21.3.2.2 Math.acos ( x )
This function returns the inverse cosine of x. The result is expressed in radians
and is in the
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is
NaN , n >1 𝔽, or n <-1 𝔽, returnNaN . - If n is
1 𝔽, return+0 𝔽. - Return an
implementation-approximated Number value representing the inverse cosine ofℝ (n).
21.3.2.3 Math.acosh ( x )
This function returns the inverse hyperbolic cosine of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is either
NaN or+∞ 𝔽, return n. - If n is
1 𝔽, return+0 𝔽. - If n <
1 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the inverse hyperbolic cosine ofℝ (n).
21.3.2.4 Math.asin ( x )
This function returns the inverse sine of x. The result is expressed in radians
and is in the
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n >
1 𝔽 or n <-1 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the inverse sine ofℝ (n).
21.3.2.5 Math.asinh ( x )
This function returns the inverse hyperbolic sine of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - Return an
implementation-approximated Number value representing the inverse hyperbolic sine ofℝ (n).
21.3.2.6 Math.atan ( x )
This function returns the inverse tangent of x. The result is expressed in radians
and is in the
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n is
+∞ 𝔽, return animplementation-approximated Number value representing π / 2. - If n is
-∞ 𝔽, return animplementation-approximated Number value representing -π / 2. - Return an
implementation-approximated Number value representing the inverse tangent ofℝ (n).
21.3.2.7 Math.atanh ( x )
This function returns the inverse hyperbolic tangent of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n >
1 𝔽 or n <-1 𝔽, returnNaN . - If n is
1 𝔽, return+∞ 𝔽. - If n is
-1 𝔽, return-∞ 𝔽. - Return an
implementation-approximated Number value representing the inverse hyperbolic tangent ofℝ (n).
21.3.2.8 Math.atan2 ( y, x )
This function returns the inverse tangent of the quotient
It performs the following steps when called:
- Let ny be ?
ToNumber (y). - Let nx be ?
ToNumber (x). - If ny is
NaN or nx isNaN , returnNaN . - If ny is
+∞ 𝔽, then- If nx is
+∞ 𝔽, return animplementation-approximated Number value representing π / 4. - If nx is
-∞ 𝔽, return animplementation-approximated Number value representing 3π / 4. - Return an
implementation-approximated Number value representing π / 2.
- If nx is
- If ny is
-∞ 𝔽, then- If nx is
+∞ 𝔽, return animplementation-approximated Number value representing -π / 4. - If nx is
-∞ 𝔽, return animplementation-approximated Number value representing -3π / 4. - Return an
implementation-approximated Number value representing -π / 2.
- If nx is
- If ny is
+0 𝔽, then- If nx >
+0 𝔽 or nx is+0 𝔽, return+0 𝔽. - Return an
implementation-approximated Number value representing π.
- If nx >
- If ny is
-0 𝔽, then- If nx >
+0 𝔽 or nx is+0 𝔽, return-0 𝔽. - Return an
implementation-approximated Number value representing -π.
- If nx >
Assert : ny isfinite and is neither+0 𝔽 nor-0 𝔽.- If ny >
+0 𝔽, then- If nx is
+∞ 𝔽, return+0 𝔽. - If nx is
-∞ 𝔽, return animplementation-approximated Number value representing π. - If nx is either
+0 𝔽 or-0 𝔽, return animplementation-approximated Number value representing π / 2.
- If nx is
- If ny <
-0 𝔽, then- If nx is
+∞ 𝔽, return-0 𝔽. - If nx is
-∞ 𝔽, return animplementation-approximated Number value representing -π. - If nx is either
+0 𝔽 or-0 𝔽, return animplementation-approximated Number value representing -π / 2.
- If nx is
Assert : nx isfinite and is neither+0 𝔽 nor-0 𝔽.- Let r be the inverse tangent of
abs (ℝ (ny) /ℝ (nx)). - If nx <
-0 𝔽, then- If ny >
+0 𝔽, set r to π - r. - Else, set r to -π + r.
- If ny >
- Else,
- If ny <
-0 𝔽, set r to -r.
- If ny <
- Return an
implementation-approximated Number value representing r.
21.3.2.9 Math.cbrt ( x )
This function returns the cube root of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - Return an
implementation-approximated Number value representing the cube root ofℝ (n).
21.3.2.10 Math.ceil ( x )
This function returns the smallest (closest to -∞)
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - If n <
-0 𝔽 and n >-1 𝔽, return-0 𝔽. - If n is an
integral Number , return n. - Return the smallest (closest to -∞)
integral Number value that is not less than n.
The value of Math.ceil(x) is the same as the value of
-Math.floor(-x).
21.3.2.11 Math.clz32 ( x )
This function performs the following steps when called:
If n is either
21.3.2.12 Math.cos ( x )
This function returns the cosine of x. The argument is expressed in radians.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite , returnNaN . - If n is either
+0 𝔽 or-0 𝔽, return1 𝔽. - Return an
implementation-approximated Number value representing the cosine ofℝ (n).
21.3.2.13 Math.cosh ( x )
This function returns the hyperbolic cosine of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is
NaN , returnNaN . - If n is either
+∞ 𝔽 or-∞ 𝔽, return+∞ 𝔽. - If n is either
+0 𝔽 or-0 𝔽, return1 𝔽. - Return an
implementation-approximated Number value representing the hyperbolic cosine ofℝ (n).
The value of Math.cosh(x) is the same as the value of
(Math.exp(x) + Math.exp(-x)) / 2.
21.3.2.14 Math.exp ( x )
This function returns the exponential function of x (e raised to the power of x, where e is the base of the natural logarithms).
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is either
NaN or+∞ 𝔽, return n. - If n is either
+0 𝔽 or-0 𝔽, return1 𝔽. - If n is
-∞ 𝔽, return+0 𝔽. - Return an
implementation-approximated Number value representing the exponential function ofℝ (n).
21.3.2.15 Math.expm1 ( x )
This function returns the result of subtracting 1 from the exponential function of x (e raised to the power of x, where e is the base of the natural logarithms). The result is computed in a way that is accurate even when the value of x is close to 0.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽,-0 𝔽, or+∞ 𝔽, return n. - If n is
-∞ 𝔽, return-1 𝔽. - Let exp be the exponential function of
ℝ (n). - Return an
implementation-approximated Number value representing exp - 1.
21.3.2.16 Math.floor ( x )
This function returns the greatest (closest to +∞)
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - If n <
1 𝔽 and n >+0 𝔽, return+0 𝔽. - If n is an
integral Number , return n. - Return the greatest (closest to +∞)
integral Number value that is not greater than n.
The value of Math.floor(x) is the same as the value of
-Math.ceil(-x).
21.3.2.17 Math.fround ( x )
This function performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is
NaN , returnNaN . - If n is one of
+0 𝔽,-0 𝔽,+∞ 𝔽, or-∞ 𝔽, return n. - Let n32 be the result of converting n to
IEEE 754-2019 binary32 format using roundTiesToEven mode. - Let n64 be the result of converting n32 to
IEEE 754-2019 binary64 format. - Return the ECMAScript Number value corresponding to n64.
21.3.2.18 Math.f16round ( x )
This function performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is
NaN , returnNaN . - If n is one of
+0 𝔽,-0 𝔽,+∞ 𝔽, or-∞ 𝔽, return n. - Let n16 be the result of converting n to
IEEE 754-2019 binary16 format using roundTiesToEven mode. - Let n64 be the result of converting n16 to
IEEE 754-2019 binary64 format. - Return the ECMAScript Number value corresponding to n64.
This operation is not the same as casting to binary32 and then to binary16 because of
the possibility of double-rounding: consider the number k =
Not all platforms provide native support for casting from binary64 to binary16. There are various libraries which can provide this, including the MIT-licensed half library. Alternatively, it is possible to first cast from binary64 to binary32 under roundTiesToEven and then check whether the result could lead to incorrect double-rounding. The cases which could can be handled explicitly by adjusting the mantissa of the binary32 value so that it is the value which would be produced by performing the initial cast under roundTiesToOdd. Casting the adjusted value to binary16 under roundTiesToEven then produces the correct value.
21.3.2.19 Math.hypot ( ...args )
Given zero or more arguments, this function returns the square root of the sum of squares of its arguments.
It performs the following steps when called:
- Let coerced be a new empty
List . - For each element arg of args, do
- Let n be ?
ToNumber (arg). - Append n to coerced.
- Let n be ?
- For each element number of coerced, do
- If number is either
+∞ 𝔽 or-∞ 𝔽, return+∞ 𝔽.
- If number is either
- Let onlyZero be
true . - For each element number of coerced, do
- If number is
NaN , returnNaN . - If number is neither
+0 𝔽 nor-0 𝔽, set onlyZero tofalse .
- If number is
- If onlyZero is
true , return+0 𝔽. - Return an
implementation-approximated Number value representing the square root of the sum of squares of themathematical values of the elements of coerced.
The
Implementations should take care to avoid the loss of precision from overflows and underflows that are prone to occur in naive implementations when this function is called with two or more arguments.
21.3.2.20 Math.imul ( x, y )
This function performs the following steps when called:
21.3.2.21 Math.log ( x )
This function returns the natural logarithm of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is either
NaN or+∞ 𝔽, return n. - If n is
1 𝔽, return+0 𝔽. - If n is either
+0 𝔽 or-0 𝔽, return-∞ 𝔽. - If n <
-0 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the natural logarithm ofℝ (n).
21.3.2.22 Math.log1p ( x )
This function returns the natural logarithm of 1 + x. The result is computed in a way that is accurate even when the value of x is close to zero.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽,-0 𝔽, or+∞ 𝔽, return n. - If n is
-1 𝔽, return-∞ 𝔽. - If n <
-1 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the natural logarithm of 1 +ℝ (n).
21.3.2.23 Math.log10 ( x )
This function returns the base 10 logarithm of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is either
NaN or+∞ 𝔽, return n. - If n is
1 𝔽, return+0 𝔽. - If n is either
+0 𝔽 or-0 𝔽, return-∞ 𝔽. - If n <
-0 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the base 10 logarithm ofℝ (n).
21.3.2.24 Math.log2 ( x )
This function returns the base 2 logarithm of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is either
NaN or+∞ 𝔽, return n. - If n is
1 𝔽, return+0 𝔽. - If n is either
+0 𝔽 or-0 𝔽, return-∞ 𝔽. - If n <
-0 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the base 2 logarithm ofℝ (n).
21.3.2.25 Math.max ( ...args )
Given zero or more arguments, this function calls
It performs the following steps when called:
- Let coerced be a new empty
List . - For each element arg of args, do
- Let n be ?
ToNumber (arg). - Append n to coerced.
- Let n be ?
- Let highest be
-∞ 𝔽. - For each element number of coerced, do
- If number is
NaN , returnNaN . - If number is
+0 𝔽 and highest is-0 𝔽, set highest to+0 𝔽. - If number > highest, set highest to number.
- If number is
- Return highest.
The comparison of values to determine the largest value is done using the
The
21.3.2.26 Math.min ( ...args )
Given zero or more arguments, this function calls
It performs the following steps when called:
- Let coerced be a new empty
List . - For each element arg of args, do
- Let n be ?
ToNumber (arg). - Append n to coerced.
- Let n be ?
- Let lowest be
+∞ 𝔽. - For each element number of coerced, do
- If number is
NaN , returnNaN . - If number is
-0 𝔽 and lowest is+0 𝔽, set lowest to-0 𝔽. - If number < lowest, set lowest to number.
- If number is
- Return lowest.
The comparison of values to determine the largest value is done using the
The
21.3.2.27 Math.pow ( base, exponent )
This function performs the following steps when called:
- Set base to ?
ToNumber (base). - Set exponent to ?
ToNumber (exponent). - Return
Number::exponentiate (base, exponent).
21.3.2.28 Math.random ( )
This function returns a Number value with positive sign, greater than or equal to
Each Math.random function created for distinct
21.3.2.29 Math.round ( x )
This function returns the Number value that is closest to x and is integral. If
two
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is anintegral Number , return n. - If n <
0.5 𝔽 and n >+0 𝔽, return+0 𝔽. - If n <
-0 𝔽 and n ≥-0.5 𝔽, return-0 𝔽. - Return the
integral Number closest to n, preferring the Number closer to +∞ in the case of a tie.
Math.round(3.5) returns 4, but Math.round(-3.5) returns -3.
The value of Math.round(x) is not always the same as the value of
Math.floor(x + 0.5). When x is
x is less than
Math.round(x) returns
Math.floor(x + 0.5) returns
Math.round(x) may also differ from
the value of Math.floor(x + 0.5)because of internal rounding when
computing x + 0.5.
21.3.2.30 Math.sign ( x )
This function returns the sign of x, indicating whether x is positive, negative, or zero.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n <
-0 𝔽, return-1 𝔽. - Return
1 𝔽.
21.3.2.31 Math.sin ( x )
This function returns the sine of x. The argument is expressed in radians.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n is either
+∞ 𝔽 or-∞ 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the sine ofℝ (n).
21.3.2.32 Math.sinh ( x )
This function returns the hyperbolic sine of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - Return an
implementation-approximated Number value representing the hyperbolic sine ofℝ (n).
The value of Math.sinh(x) is the same as the value of
(Math.exp(x) - Math.exp(-x)) / 2.
21.3.2.33 Math.sqrt ( x )
This function returns the square root of x.
It performs the following steps when called:
21.3.2.34 Math.tan ( x )
This function returns the tangent of x. The argument is expressed in radians.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n is either
+∞ 𝔽 or-∞ 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the tangent ofℝ (n).
21.3.2.35 Math.tanh ( x )
This function returns the hyperbolic tangent of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n is
+∞ 𝔽, return1 𝔽. - If n is
-∞ 𝔽, return-1 𝔽. - Return an
implementation-approximated Number value representing the hyperbolic tangent ofℝ (n).
The value of Math.tanh(x) is the same as the value of
(Math.exp(x) - Math.exp(-x)) / (Math.exp(x) + Math.exp(-x)).
21.3.2.36 Math.trunc ( x )
This function returns the integral part of the number x, removing any fractional digits. If x is already integral, the result is x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - If n <
1 𝔽 and n >+0 𝔽, return+0 𝔽. - If n <
-0 𝔽 and n >-1 𝔽, return-0 𝔽. - Return the
integral Number nearest n in the direction of+0 𝔽.
21.4 Date Objects
21.4.1 Overview of Date Objects and Definitions of Abstract Operations
The following
21.4.1.1 Time Values and Time Range
Time measurement in ECMAScript is analogous to time measurement in POSIX, in particular sharing definition in terms of the proleptic Gregorian calendar, an epoch of midnight at the beginning of 1 January 1970 UTC, and an accounting of every day as comprising exactly 86,400 seconds (each of which is 1000 milliseconds long).
An ECMAScript time value
Time values do not account for UTC leap seconds—there are no time values representing instants within positive leap seconds, and there are time values representing instants removed from the UTC timeline by negative leap seconds. However, the definition of time values nonetheless yields piecewise alignment with UTC, with discontinuities only at leap second boundaries and zero difference outside of leap seconds.
A Number can exactly represent all
The exact moment of midnight at the beginning of 1 January 1970 UTC is represented by the
time value
In the proleptic Gregorian calendar, leap years are precisely those which are both divisible by 4 and either divisible by 400 or not divisible by 100.
The 400 year cycle of the proleptic Gregorian calendar contains 97 leap years. This yields an average of 365.2425 days per year, which is 31,556,952,000 milliseconds. Therefore, the maximum range a Number could represent exactly with millisecond precision is approximately -285,426 to 285,426 years relative to 1970. The smaller range supported by a time value as specified in this section is approximately -273,790 to 273,790 years relative to 1970.
21.4.1.2 Time-related Constants
These constants are referenced by algorithms in the following sections.
21.4.1.3 Day ( t )
The abstract operation Day takes argument t (a
21.4.1.4 TimeWithinDay ( t )
The abstract operation TimeWithinDay takes argument t (a
21.4.1.5 DaysInYear ( y )
The abstract operation DaysInYear takes argument y (an
21.4.1.6 DayFromYear ( y )
The abstract operation DayFromYear takes argument y (an
- Let ry be
ℝ (y). - NOTE: In the following steps,
numYears1, numYears4, numYears100, and
numYears400 represent the number of years divisible by 1, 4, 100, and
400, respectively, that occur between the
epoch and the start of year y. The number is negative if y is before theepoch . - Let numYears1 be (ry - 1970).
- Let numYears4 be
floor ((ry - 1969) / 4). - Let numYears100 be
floor ((ry - 1901) / 100). - Let numYears400 be
floor ((ry - 1601) / 400). - Return
𝔽 (365 × numYears1 + numYears4 - numYears100 + numYears400).
21.4.1.7 TimeFromYear ( y )
The abstract operation TimeFromYear takes argument y (an
- Return
msPerDay ×DayFromYear (y).
21.4.1.8 YearFromTime ( t )
The abstract operation YearFromTime takes argument t (a
- Return the largest
integral Number y (closest to +∞) such thatTimeFromYear (y) ≤ t.
21.4.1.9 DayWithinYear ( t )
The abstract operation DayWithinYear takes argument t (a
- Return
Day (t) -DayFromYear (YearFromTime (t)).
21.4.1.10 InLeapYear ( t )
The abstract operation InLeapYear takes argument t (a
- If
DaysInYear (YearFromTime (t)) is366 𝔽, return1 𝔽; else return+0 𝔽.
21.4.1.11 MonthFromTime ( t )
The abstract operation MonthFromTime takes argument t (a
- Let inLeapYear be
InLeapYear (t). - Let dayWithinYear be
DayWithinYear (t). - If dayWithinYear <
31 𝔽, return+0 𝔽. - If dayWithinYear <
59 𝔽 + inLeapYear, return1 𝔽. - If dayWithinYear <
90 𝔽 + inLeapYear, return2 𝔽. - If dayWithinYear <
120 𝔽 + inLeapYear, return3 𝔽. - If dayWithinYear <
151 𝔽 + inLeapYear, return4 𝔽. - If dayWithinYear <
181 𝔽 + inLeapYear, return5 𝔽. - If dayWithinYear <
212 𝔽 + inLeapYear, return6 𝔽. - If dayWithinYear <
243 𝔽 + inLeapYear, return7 𝔽. - If dayWithinYear <
273 𝔽 + inLeapYear, return8 𝔽. - If dayWithinYear <
304 𝔽 + inLeapYear, return9 𝔽. - If dayWithinYear <
334 𝔽 + inLeapYear, return10 𝔽. Assert : dayWithinYear <365 𝔽 + inLeapYear.- Return
11 𝔽.
21.4.1.12 DateFromTime ( t )
The abstract operation DateFromTime takes argument t (a
- Let inLeapYear be
InLeapYear (t). - Let dayWithinYear be
DayWithinYear (t). - Let month be
MonthFromTime (t). - If month is
+0 𝔽, return dayWithinYear +1 𝔽. - If month is
1 𝔽, return dayWithinYear -30 𝔽. - If month is
2 𝔽, return dayWithinYear -58 𝔽 - inLeapYear. - If month is
3 𝔽, return dayWithinYear -89 𝔽 - inLeapYear. - If month is
4 𝔽, return dayWithinYear -119 𝔽 - inLeapYear. - If month is
5 𝔽, return dayWithinYear -150 𝔽 - inLeapYear. - If month is
6 𝔽, return dayWithinYear -180 𝔽 - inLeapYear. - If month is
7 𝔽, return dayWithinYear -211 𝔽 - inLeapYear. - If month is
8 𝔽, return dayWithinYear -242 𝔽 - inLeapYear. - If month is
9 𝔽, return dayWithinYear -272 𝔽 - inLeapYear. - If month is
10 𝔽, return dayWithinYear -303 𝔽 - inLeapYear. Assert : month is11 𝔽.- Return dayWithinYear -
333 𝔽 - inLeapYear.
21.4.1.13 WeekDay ( t )
The abstract operation WeekDay takes argument t (a
21.4.1.14 HourFromTime ( t )
The abstract operation HourFromTime takes argument t (a
21.4.1.15 MinFromTime ( t )
The abstract operation MinFromTime takes argument t (a
- Return
𝔽 (floor (ℝ (t /msPerMinute ))modulo MinutesPerHour ).
21.4.1.16 SecFromTime ( t )
The abstract operation SecFromTime takes argument t (a
- Return
𝔽 (floor (ℝ (t /msPerSecond ))modulo SecondsPerMinute ).
21.4.1.17 msFromTime ( t )
The abstract operation msFromTime takes argument t (a
- Return
𝔽 (ℝ (t)modulo ℝ (msPerSecond )).
21.4.1.18 GetUTCEpochNanoseconds ( year, month, day, hour, minute, second, millisecond, microsecond, nanosecond )
The abstract operation GetUTCEpochNanoseconds takes arguments year (an
21.4.1.19 Time Zone Identifiers
Time zones in ECMAScript are represented by time zone identifiers, which are Strings composed entirely of code
units in the
A primary time zone identifier is the preferred identifier for an available named time zone. A non-primary time zone identifier is an identifier for an available named time zone that is not a primary time zone identifier. An available named time zone identifier is either a primary time zone identifier or a non-primary time zone identifier. Each available named time zone identifier is associated with exactly one available named time zone. Each available named time zone is associated with exactly one primary time zone identifier and zero or more non-primary time zone identifiers.
ECMAScript implementations must support an available named time zone with the identifier
Implementations that follow the requirements for time zones as described in the ECMA-402
Internationalization API specification are called time zone aware.
Time zone aware implementations must support available named time zones corresponding to the
Zone and Link names of the IANA Time Zone Database, and only such names.
In time zone aware implementations, a primary time zone identifier is a Zone name, and a
non-primary time zone identifier is a Link name, respectively, in the IANA Time Zone
Database except as specifically overridden by
21.4.1.20 GetNamedTimeZoneEpochNanoseconds ( timeZoneIdentifier, year, month, day, hour, minute, second, millisecond, microsecond, nanosecond )
The
When the input represents a local time occurring more than once because of a negative time
zone transition (e.g. when daylight saving time ends or the time zone offset is decreased
due to a time zone rule change), the returned
The default implementation of GetNamedTimeZoneEpochNanoseconds, to be used for ECMAScript implementations that do not include local political rules for any time zones, performs the following steps when called:
Assert : timeZoneIdentifier is"UTC" .- Let epochNanoseconds be
GetUTCEpochNanoseconds (year, month, day, hour, minute, second, millisecond, microsecond, nanosecond). - Return « epochNanoseconds ».
It is required for
1:30 AM on 5 November 2017 in America/New_York is repeated twice, so
GetNamedTimeZoneEpochNanoseconds(
2:30 AM on 12 March 2017 in America/New_York does not exist, so
GetNamedTimeZoneEpochNanoseconds(
21.4.1.21 GetNamedTimeZoneOffsetNanoseconds ( timeZoneIdentifier, epochNanoseconds )
The
The returned
The default implementation of GetNamedTimeZoneOffsetNanoseconds, to be used for ECMAScript implementations that do not include local political rules for any time zones, performs the following steps when called:
Assert : timeZoneIdentifier is"UTC" .- Return 0.
Time zone offset values may be positive or negative.
21.4.1.22 Time Zone Identifier Record
A Time Zone Identifier
Record is a
Time Zone Identifier Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Identifier]] | a String | An |
| [[PrimaryIdentifier]] | a String | The |
If [[Identifier]] is a
21.4.1.23 AvailableNamedTimeZoneIdentifiers ( )
The
- If the implementation does not include local political rules for any time zones,
then
- Return « the
Time Zone Identifier Record { [[Identifier]]:"UTC" , [[PrimaryIdentifier]]:"UTC" } ».
- Return « the
- Let identifiers be the
List of uniqueavailable named time zone identifiers , sorted according tolexicographic code unit order . - Let result be a new empty
List . - For each element identifier of identifiers, do
- Let primary be identifier.
- If identifier is a
non-primary time zone identifier in this implementation and identifier is not"UTC" , then- Set primary to the
primary time zone identifier associated with identifier. - NOTE: An implementation may need to resolve identifier
iteratively to obtain the
primary time zone identifier .
- Set primary to the
- Let record be the
Time Zone Identifier Record { [[Identifier]]: identifier, [[PrimaryIdentifier]]: primary }. - Append record to result.
Assert : result contains aTime Zone Identifier Record r such that r.[[Identifier]] is"UTC" and r.[[PrimaryIdentifier]] is"UTC" .- Return result.
21.4.1.24 SystemTimeZoneIdentifier ( )
The
- If the implementation only supports the UTC time zone, return
"UTC" . - Let systemTimeZoneString be the String representing the
host environment 's current time zone, either aprimary time zone identifier or anoffset time zone identifier. - Return systemTimeZoneString.
To ensure the level of functionality that implementations commonly provide in the
methods of the Date object, it is recommended that SystemTimeZoneIdentifier return
an IANA time zone name corresponding to the
For example, if the
21.4.1.25 LocalTime ( t )
The abstract operation LocalTime takes argument t (a
- Let systemTimeZoneIdentifier be
SystemTimeZoneIdentifier (). - If
IsTimeZoneOffsetString (systemTimeZoneIdentifier) istrue , then- Let offsetNs be
ParseTimeZoneOffsetString (systemTimeZoneIdentifier).
- Let offsetNs be
- Else,
- Let offsetNs be
GetNamedTimeZoneOffsetNanoseconds (systemTimeZoneIdentifier,ℤ (ℝ (t) × 106)).
- Let offsetNs be
- Let offsetMs be
truncate (offsetNs / 106). - Return t +
𝔽 (offsetMs).
If political rules for the local time t are not available within the
implementation, the result is t because
It is required for
Two different input
21.4.1.26 UTC ( t )
The abstract operation UTC takes argument t (a Number) and returns a
- If t is not
finite , returnNaN . - Let systemTimeZoneIdentifier be
SystemTimeZoneIdentifier (). - If
IsTimeZoneOffsetString (systemTimeZoneIdentifier) istrue , then- Let offsetNs be
ParseTimeZoneOffsetString (systemTimeZoneIdentifier).
- Let offsetNs be
- Else,
- Let possibleInstants be
GetNamedTimeZoneEpochNanoseconds (systemTimeZoneIdentifier,ℝ (YearFromTime (t)),ℝ (MonthFromTime (t)) + 1,ℝ (DateFromTime (t)),ℝ (HourFromTime (t)),ℝ (MinFromTime (t)),ℝ (SecFromTime (t)),ℝ (msFromTime (t)), 0, 0). - NOTE: The following steps ensure that when t represents local time repeating multiple times at a negative time zone transition (e.g. when the daylight saving time ends or the time zone offset is decreased due to a time zone rule change) or skipped local time at a positive time zone transition (e.g. when the daylight saving time starts or the time zone offset is increased due to a time zone rule change), t is interpreted using the time zone offset before the transition.
- If possibleInstants is not empty, then
- Let disambiguatedInstant be possibleInstants[0].
- Else,
- NOTE: t represents a local time skipped at a positive time zone transition (e.g. due to daylight saving time starting or a time zone rule change increasing the UTC offset).
- Let possibleInstantsBefore be
GetNamedTimeZoneEpochNanoseconds (systemTimeZoneIdentifier,ℝ (YearFromTime (tBefore)),ℝ (MonthFromTime (tBefore)) + 1,ℝ (DateFromTime (tBefore)),ℝ (HourFromTime (tBefore)),ℝ (MinFromTime (tBefore)),ℝ (SecFromTime (tBefore)),ℝ (msFromTime (tBefore)), 0, 0), where tBefore is the largestintegral Number < t for which possibleInstantsBefore is not empty (i.e., tBefore represents the last local time before the transition). - Let disambiguatedInstant be the last element of possibleInstantsBefore.
- Let offsetNs be
GetNamedTimeZoneOffsetNanoseconds (systemTimeZoneIdentifier, disambiguatedInstant).
- Let possibleInstants be
- Let offsetMs be
truncate (offsetNs / 106). - Return t -
𝔽 (offsetMs).
Input t is nominally a
If political rules for the local time t are not available within the
implementation, the result is t because
It is required for
1:30 AM on 5 November 2017 in America/New_York is repeated twice (fall backward),
but it must be interpreted as 1:30 AM UTC-04 instead of 1:30 AM UTC-05.
In UTC(
2:30 AM on 12 March 2017 in America/New_York does not exist, but it must be
interpreted as 2:30 AM UTC-05 (equivalent to 3:30 AM UTC-04).
In UTC(
21.4.1.27 MakeTime ( hour, min, sec, ms )
The abstract operation MakeTime takes arguments hour (a Number), min (a Number), sec (a Number), and ms (a Number) and returns a Number. It calculates a number of milliseconds. It performs the following steps when called:
- If hour is not
finite , min is notfinite , sec is notfinite , or ms is notfinite , returnNaN . - Let h be
𝔽 (!ToIntegerOrInfinity (hour)). - Let m be
𝔽 (!ToIntegerOrInfinity (min)). - Let s be
𝔽 (!ToIntegerOrInfinity (sec)). - Let milli be
𝔽 (!ToIntegerOrInfinity (ms)). - Return ((h ×
msPerHour + m ×msPerMinute ) + s ×msPerSecond ) + milli.
The arithmetic in MakeTime is floating-point arithmetic, which is not associative, so the operations must be performed in the correct order.
21.4.1.28 MakeDay ( year, month, date )
The abstract operation MakeDay takes arguments year (a Number), month (a Number), and date (a Number) and returns a Number. It calculates a number of days. It performs the following steps when called:
- If year is not
finite , month is notfinite , or date is notfinite , returnNaN . - Let y be
𝔽 (!ToIntegerOrInfinity (year)). - Let m be
𝔽 (!ToIntegerOrInfinity (month)). - Let dt be
𝔽 (!ToIntegerOrInfinity (date)). - Let ym be y +
𝔽 (floor (ℝ (m) / 12)). - If ym is not
finite , returnNaN . - Let mn be
𝔽 (ℝ (m)modulo 12). - Find a
finite time value t such thatYearFromTime (t) is ym,MonthFromTime (t) is mn, andDateFromTime (t) is1 𝔽; but if this is not possible (because some argument is out of range), returnNaN . - Return
Day (t) + dt -1 𝔽.
21.4.1.29 MakeDate ( day, time )
The abstract operation MakeDate takes arguments day (a Number) and time (a Number) and returns a Number. It calculates a number of milliseconds. It performs the following steps when called:
21.4.1.30 MakeFullYear ( year )
The abstract operation MakeFullYear takes argument year (a Number) and returns an
- If year is
NaN , returnNaN . - Let truncated be !
ToIntegerOrInfinity (year). - If truncated is in the
inclusive interval from 0 to 99, return1900 𝔽 +𝔽 (truncated). - Return
𝔽 (truncated).
21.4.1.31 TimeClip ( time )
The abstract operation TimeClip takes argument time (a Number) and returns a Number. It calculates a number of milliseconds. It performs the following steps when called:
- If time is not
finite , returnNaN . - If
abs (ℝ (time)) > 8.64 × 1015, returnNaN . - Return
𝔽 (!ToIntegerOrInfinity (time)).
21.4.1.32 Date Time String Format
ECMAScript defines a string interchange format for date-times based upon a simplification of
the ISO 8601 calendar date extended format. The format is as follows:
YYYY-MM-DDTHH:mm:ss.sssZ
Where the elements are as follows:
YYYY
|
is the year in the proleptic Gregorian calendar as four decimal digits from
0000 to 9999, or as an |
-
|
|
MM
|
is the month of the year as two decimal digits from 01 (January) to 12 (December). |
DD
|
is the day of the month as two decimal digits from 01 to 31. |
T
|
|
HH
|
is the number of complete hours that have passed since midnight as two decimal digits from 00 to 24. |
:
|
|
mm
|
is the number of complete minutes since the start of the hour as two decimal digits from 00 to 59. |
ss
|
is the number of complete seconds since the start of the minute as two decimal digits from 00 to 59. |
.
|
|
sss
|
is the number of complete milliseconds since the start of the second as three decimal digits. |
Z
|
is the UTC offset representation specified as HH:mm (a
subset of the |
This format includes date-only forms:
YYYY
YYYY-MM
YYYY-MM-DD
It also includes “date-time” forms that consist of one of the above date-only forms immediately followed by one of the following time forms with an optional UTC offset representation appended:
THH:mm
THH:mm:ss
THH:mm:ss.sss
A string containing out-of-bounds or nonconforming elements is not a valid instance of this format.
As every day both starts and ends with midnight, the two notations 00:00
and 24:00 are available to distinguish the two midnights that can be
associated with one date. This means that the following two notations refer to
exactly the same point in time: 1995-02-04T24:00 and
1995-02-05T00:00. This interpretation of the latter form as "end of a
calendar day" is consistent with ISO 8601, even though that specification reserves
it for describing time intervals and does not permit it within representations of
single points in time.
There exists no international standard that specifies abbreviations for civil time zones like CET, EST, etc. and sometimes the same abbreviation is even used for two very different time zones. For this reason, both ISO 8601 and this format specify numeric representations of time zone offsets.
21.4.1.32.1 Expanded Years
Covering the full Date.parse
Examples of date-
| -271821-04-20T00:00:00Z | 271822 B.C. |
| -000001-01-01T00:00:00Z | 2 B.C. |
| +000000-01-01T00:00:00Z | 1 B.C. |
| +000001-01-01T00:00:00Z | 1 A.D. |
| +001970-01-01T00:00:00Z | 1970 A.D. |
| +002009-12-15T00:00:00Z | 2009 A.D. |
| +275760-09-13T00:00:00Z | 275760 A.D. |
21.4.1.33 Time Zone Offset String Format
ECMAScript defines a string interchange format for UTC offsets, derived from ISO 8601. The format is described by the following grammar.
Syntax
21.4.1.33.1 IsTimeZoneOffsetString ( offsetString )
The abstract operation IsTimeZoneOffsetString takes argument offsetString (a
String) and returns a Boolean. The return value indicates whether
offsetString conforms to the grammar given by
21.4.1.33.2 ParseTimeZoneOffsetString ( offsetString )
The abstract operation ParseTimeZoneOffsetString takes argument offsetString
(a String) and returns an
- Let parseResult be
ParseText (offsetString,UTCOffset ). Assert : parseResult is not aList of errors.Assert : parseResult contains aASCIISign Parse Node .- Let parsedSign be the
source text matched by theASCIISign Parse Node contained within parseResult. - If parsedSign is the single code point U+002D (HYPHEN-MINUS), then
- Let sign be -1.
- Else,
- Let sign be 1.
- NOTE: Applications of
StringToNumber below do not lose precision, since each of the parsed values is guaranteed to be a sufficiently short string of decimal digits. Assert : parseResult contains anHour Parse Node .- Let parsedHours be the
source text matched by theHour Parse Node contained within parseResult. - Let hours be
ℝ (StringToNumber (CodePointsToString (parsedHours))). - If parseResult does not contain a
MinuteSecond Parse Node , then- Let minutes be 0.
- Else,
- Let parsedMinutes be the
source text matched by the firstMinuteSecond Parse Node contained within parseResult. - Let minutes be
ℝ (StringToNumber (CodePointsToString (parsedMinutes))).
- Let parsedMinutes be the
- If parseResult does not contain two
MinuteSecond Parse Nodes , then- Let seconds be 0.
- Else,
- Let parsedSeconds be the
source text matched by the secondMinuteSecond Parse Node contained within parseResult. - Let seconds be
ℝ (StringToNumber (CodePointsToString (parsedSeconds))).
- Let parsedSeconds be the
- If parseResult does not contain a
TemporalDecimalFraction Parse Node , then- Let nanoseconds be 0.
- Else,
- Let parsedFraction be the
source text matched by theTemporalDecimalFraction Parse Node contained within parseResult. - Let fraction be the
string-concatenation ofCodePointsToString (parsedFraction) and"000000000" . - Let nanosecondsString be the
substring of fraction from 1 to 10. - Let nanoseconds be
ℝ (StringToNumber (nanosecondsString)).
- Let parsedFraction be the
- Return sign × (((hours × 60 + minutes) × 60 + seconds) × 109 + nanoseconds).
21.4.2 The Date Constructor
The Date
- is %Date%.
- is the initial value of the
"Date" property of theglobal object . - creates and initializes a new Date when called as a
constructor . - returns a String representing the current time (UTC) when called as a function rather than
as a
constructor . - is a function whose behaviour differs based upon the number and types of its arguments.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Date behaviour must include asupercall to the Dateconstructor to create and initialize the subclass instance with a [[DateValue]] internal slot.
21.4.2.1 Date ( ...values )
This function performs the following steps when called:
- If NewTarget is
undefined , then- Let now be the
time value (UTC) identifying the current time. - Return
ToDateString (now).
- Let now be the
- Let numberOfArgs be the number of elements in values.
- If numberOfArgs = 0, then
- Let dv be the
time value (UTC) identifying the current time.
- Let dv be the
- Else if numberOfArgs = 1, then
- Let value be values[0].
- If value
is an Object and value has a [[DateValue]] internal slot, then- Let tv be value.[[DateValue]].
- Else,
- Let v be ?
ToPrimitive (value). - If v
is a String , thenAssert : The next step never returns anabrupt completion because vis a String .- Let tv be the result of parsing v as a
date, in exactly the same manner as for the
parsemethod (21.4.3.2 ).
- Else,
- Let tv be ?
ToNumber (v).
- Let tv be ?
- Let v be ?
- Let dv be
TimeClip (tv).
- Else,
Assert : numberOfArgs ≥ 2.- Let y be ?
ToNumber (values[0]). - Let m be ?
ToNumber (values[1]). - If numberOfArgs > 2, let dt be ?
ToNumber (values[2]); else let dt be1 𝔽. - If numberOfArgs > 3, let h be ?
ToNumber (values[3]); else let h be+0 𝔽. - If numberOfArgs > 4, let min be ?
ToNumber (values[4]); else let min be+0 𝔽. - If numberOfArgs > 5, let s be ?
ToNumber (values[5]); else let s be+0 𝔽. - If numberOfArgs > 6, let milli be ?
ToNumber (values[6]); else let milli be+0 𝔽. - Let yr be
MakeFullYear (y). - Let finalDate be
MakeDate (MakeDay (yr, m, dt),MakeTime (h, min, s, milli)). - Let dv be
TimeClip (UTC (finalDate)).
- Let O be ?
OrdinaryCreateFromConstructor (NewTarget,"%Date.prototype%" , « [[DateValue]] »). - Set O.[[DateValue]] to dv.
- Return O.
21.4.3 Properties of the Date Constructor
The Date
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"length" property whose value is7 𝔽. - has the following properties:
21.4.3.1 Date.now ( )
This function returns the
21.4.3.2 Date.parse ( string )
This function applies the
If the String conforms to the MM or
DD elements are absent, HH, mm, or ss elements are absent,
sss element is absent,
If x is any Date whose milliseconds amount is zero within a particular
implementation of ECMAScript, then all of the following expressions should produce the same
numeric value in that implementation, if all the properties referenced have their initial
values:
x.valueOf()
Date.parse(x.toString())
Date.parse(x.toUTCString())
Date.parse(x.toISOString())However, the expression
Date.parse(x.toLocaleString())is not required to produce the same Number value as the preceding three expressions and, in
general, the value produced by this function is toString or toUTCString
method.
21.4.3.3 Date.prototype
The initial value of Date.prototype is the
This property has the attributes { [[Writable]]:
21.4.3.4 Date.UTC ( year [ , month [ , date [ , hours [ , minutes [ , seconds [ , ms ] ] ] ] ] ] )
This function performs the following steps when called:
- Let y be ?
ToNumber (year). - If month is present, let m be ?
ToNumber (month); else let m be+0 𝔽. - If date is present, let dt be ?
ToNumber (date); else let dt be1 𝔽. - If hours is present, let h be ?
ToNumber (hours); else let h be+0 𝔽. - If minutes is present, let min be ?
ToNumber (minutes); else let min be+0 𝔽. - If seconds is present, let s be ?
ToNumber (seconds); else let s be+0 𝔽. - If ms is present, let milli be ?
ToNumber (ms); else let milli be+0 𝔽. - Let yr be
MakeFullYear (y). - Return
TimeClip (MakeDate (MakeDay (yr, m, dt),MakeTime (h, min, s, milli))).
The
This function differs from the Date
21.4.4 Properties of the Date Prototype Object
The Date prototype object:
- is %Date.prototype%.
- is itself an
ordinary object . - is not a Date instance and does not have a [[DateValue]] internal slot.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% .
Unless explicitly defined otherwise, the methods of the Date prototype object defined below are
not generic and the
21.4.4.1 Date.prototype.constructor
The initial value of Date.prototype.constructor is
21.4.4.2 Date.prototype.getDate ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
DateFromTime (LocalTime (t)).
21.4.4.3 Date.prototype.getDay ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
WeekDay (LocalTime (t)).
21.4.4.4 Date.prototype.getFullYear ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
YearFromTime (LocalTime (t)).
21.4.4.5 Date.prototype.getHours ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
HourFromTime (LocalTime (t)).
21.4.4.6 Date.prototype.getMilliseconds ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
msFromTime (LocalTime (t)).
21.4.4.7 Date.prototype.getMinutes ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
MinFromTime (LocalTime (t)).
21.4.4.8 Date.prototype.getMonth ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
MonthFromTime (LocalTime (t)).
21.4.4.9 Date.prototype.getSeconds ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
SecFromTime (LocalTime (t)).
21.4.4.10 Date.prototype.getTime ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Return dateObject.[[DateValue]].
21.4.4.11 Date.prototype.getTimezoneOffset ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return (t -
LocalTime (t)) /msPerMinute .
21.4.4.12 Date.prototype.getUTCDate ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
DateFromTime (t).
21.4.4.13 Date.prototype.getUTCDay ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
WeekDay (t).
21.4.4.14 Date.prototype.getUTCFullYear ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
YearFromTime (t).
21.4.4.15 Date.prototype.getUTCHours ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
HourFromTime (t).
21.4.4.16 Date.prototype.getUTCMilliseconds ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
msFromTime (t).
21.4.4.17 Date.prototype.getUTCMinutes ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
MinFromTime (t).
21.4.4.18 Date.prototype.getUTCMonth ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
MonthFromTime (t).
21.4.4.19 Date.prototype.getUTCSeconds ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
SecFromTime (t).
21.4.4.20 Date.prototype.setDate ( date )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let dt be ?
ToNumber (date). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - Let newDate be
MakeDate (MakeDay (YearFromTime (t),MonthFromTime (t), dt),TimeWithinDay (t)). - Let u be
TimeClip (UTC (newDate)). - Set dateObject.[[DateValue]] to u.
- Return u.
21.4.4.21 Date.prototype.setFullYear ( year [ , month [ , date ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let y be ?
ToNumber (year). - If t is
NaN , set t to+0 𝔽; otherwise set t toLocalTime (t). - If month is not present, let m be
MonthFromTime (t); otherwise let m be ?ToNumber (month). - If date is not present, let dt be
DateFromTime (t); otherwise let dt be ?ToNumber (date). - Let newDate be
MakeDate (MakeDay (y, m, dt),TimeWithinDay (t)). - Let u be
TimeClip (UTC (newDate)). - Set dateObject.[[DateValue]] to u.
- Return u.
The
If month is not present, this method behaves as if month was
present with the value getMonth(). If date is not present,
it behaves as if date was present with the value getDate().
21.4.4.22 Date.prototype.setHours ( hour [ , min [ , sec [ , ms ] ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let h be ?
ToNumber (hour). - If min is present, let m be ?
ToNumber (min). - If sec is present, let s be ?
ToNumber (sec). - If ms is present, let milli be ?
ToNumber (ms). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - If min is not present, let m be
MinFromTime (t). - If sec is not present, let s be
SecFromTime (t). - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (h, m, s, milli)). - Let u be
TimeClip (UTC (date)). - Set dateObject.[[DateValue]] to u.
- Return u.
The
If min is not present, this method behaves as if min was
present with the value getMinutes(). If sec is not present,
it behaves as if sec was present with the value
getSeconds(). If ms is not present, it behaves as if
ms was present with the value getMilliseconds().
21.4.4.23 Date.prototype.setMilliseconds ( ms )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Set ms to ?
ToNumber (ms). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - Let time be
MakeTime (HourFromTime (t),MinFromTime (t),SecFromTime (t), ms). - Let u be
TimeClip (UTC (MakeDate (Day (t), time))). - Set dateObject.[[DateValue]] to u.
- Return u.
21.4.4.24 Date.prototype.setMinutes ( min [ , sec [ , ms ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let m be ?
ToNumber (min). - If sec is present, let s be ?
ToNumber (sec). - If ms is present, let milli be ?
ToNumber (ms). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - If sec is not present, let s be
SecFromTime (t). - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (HourFromTime (t), m, s, milli)). - Let u be
TimeClip (UTC (date)). - Set dateObject.[[DateValue]] to u.
- Return u.
The
If sec is not present, this method behaves as if sec was
present with the value getSeconds(). If ms is not present,
this behaves as if ms was present with the value
getMilliseconds().
21.4.4.25 Date.prototype.setMonth ( month [ , date ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let m be ?
ToNumber (month). - If date is present, let dt be ?
ToNumber (date). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - If date is not present, let dt be
DateFromTime (t). - Let newDate be
MakeDate (MakeDay (YearFromTime (t), m, dt),TimeWithinDay (t)). - Let u be
TimeClip (UTC (newDate)). - Set dateObject.[[DateValue]] to u.
- Return u.
The
If date is not present, this method behaves as if date was
present with the value getDate().
21.4.4.26 Date.prototype.setSeconds ( sec [ , ms ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let s be ?
ToNumber (sec). - If ms is present, let milli be ?
ToNumber (ms). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (HourFromTime (t),MinFromTime (t), s, milli)). - Let u be
TimeClip (UTC (date)). - Set dateObject.[[DateValue]] to u.
- Return u.
The
If ms is not present, this method behaves as if ms was present
with the value getMilliseconds().
21.4.4.27 Date.prototype.setTime ( time )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be ?
ToNumber (time). - Let v be
TimeClip (t). - Set dateObject.[[DateValue]] to v.
- Return v.
21.4.4.28 Date.prototype.setUTCDate ( date )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let dt be ?
ToNumber (date). - If t is
NaN , returnNaN . - Let newDate be
MakeDate (MakeDay (YearFromTime (t),MonthFromTime (t), dt),TimeWithinDay (t)). - Let v be
TimeClip (newDate). - Set dateObject.[[DateValue]] to v.
- Return v.
21.4.4.29 Date.prototype.setUTCFullYear ( year [ , month [ , date ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , set t to+0 𝔽. - Let y be ?
ToNumber (year). - If month is not present, let m be
MonthFromTime (t); otherwise let m be ?ToNumber (month). - If date is not present, let dt be
DateFromTime (t); otherwise let dt be ?ToNumber (date). - Let newDate be
MakeDate (MakeDay (y, m, dt),TimeWithinDay (t)). - Let v be
TimeClip (newDate). - Set dateObject.[[DateValue]] to v.
- Return v.
The
If month is not present, this method behaves as if month was
present with the value getUTCMonth(). If date is not
present, it behaves as if date was present with the value
getUTCDate().
21.4.4.30 Date.prototype.setUTCHours ( hour [ , min [ , sec [ , ms ] ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let h be ?
ToNumber (hour). - If min is present, let m be ?
ToNumber (min). - If sec is present, let s be ?
ToNumber (sec). - If ms is present, let milli be ?
ToNumber (ms). - If t is
NaN , returnNaN . - If min is not present, let m be
MinFromTime (t). - If sec is not present, let s be
SecFromTime (t). - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (h, m, s, milli)). - Let v be
TimeClip (date). - Set dateObject.[[DateValue]] to v.
- Return v.
The
If min is not present, this method behaves as if min was
present with the value getUTCMinutes(). If sec is not
present, it behaves as if sec was present with the value
getUTCSeconds(). If ms is not present, it behaves as if
ms was present with the value getUTCMilliseconds().
21.4.4.31 Date.prototype.setUTCMilliseconds ( ms )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Set ms to ?
ToNumber (ms). - If t is
NaN , returnNaN . - Let time be
MakeTime (HourFromTime (t),MinFromTime (t),SecFromTime (t), ms). - Let v be
TimeClip (MakeDate (Day (t), time)). - Set dateObject.[[DateValue]] to v.
- Return v.
21.4.4.32 Date.prototype.setUTCMinutes ( min [ , sec [ , ms ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let m be ?
ToNumber (min). - If sec is present, let s be ?
ToNumber (sec). - If ms is present, let milli be ?
ToNumber (ms). - If t is
NaN , returnNaN . - If sec is not present, let s be
SecFromTime (t). - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (HourFromTime (t), m, s, milli)). - Let v be
TimeClip (date). - Set dateObject.[[DateValue]] to v.
- Return v.
The
If sec is not present, this method behaves as if sec was
present with the value getUTCSeconds(). If ms is not
present, it behaves as if ms was present with the value return by
getUTCMilliseconds().
21.4.4.33 Date.prototype.setUTCMonth ( month [ , date ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let m be ?
ToNumber (month). - If date is present, let dt be ?
ToNumber (date). - If t is
NaN , returnNaN . - If date is not present, let dt be
DateFromTime (t). - Let newDate be
MakeDate (MakeDay (YearFromTime (t), m, dt),TimeWithinDay (t)). - Let v be
TimeClip (newDate). - Set dateObject.[[DateValue]] to v.
- Return v.
The
If date is not present, this method behaves as if date was
present with the value getUTCDate().
21.4.4.34 Date.prototype.setUTCSeconds ( sec [ , ms ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let s be ?
ToNumber (sec). - If ms is present, let milli be ?
ToNumber (ms). - If t is
NaN , returnNaN . - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (HourFromTime (t),MinFromTime (t), s, milli)). - Let v be
TimeClip (date). - Set dateObject.[[DateValue]] to v.
- Return v.
The
If ms is not present, this method behaves as if ms was present
with the value getUTCMilliseconds().
21.4.4.35 Date.prototype.toDateString ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let tv be dateObject.[[DateValue]].
- If tv is
NaN , return"Invalid Date" . - Let t be
LocalTime (tv). - Return
DateString (t).
21.4.4.36 Date.prototype.toISOString ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let tv be dateObject.[[DateValue]].
- If tv is
NaN , throw aRangeError exception. Assert : tv is anintegral Number .- If tv corresponds with a year that cannot be represented in the
Date Time String Format , throw aRangeError exception. - Return a String representation of tv in the
Date Time String Format on the UTC time scale, including all format elements and the UTC offset representation"Z" .
21.4.4.37 Date.prototype.toJSON ( key )
This method provides a String representation of a Date for use by JSON.stringify
(
It performs the following steps when called:
- Let O be ?
ToObject (this value). - Let tv be ?
ToPrimitive (O,number ). - If tv
is a Number and tv is notfinite , returnnull . - Return ?
Invoke (O,"toISOString" ).
The argument is ignored.
This method is intentionally generic; it does not require that its
toISOString method.
21.4.4.38 Date.prototype.toLocaleDateString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a String value. The contents of the String are
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.4.4.39 Date.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a String value. The contents of the String are
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.4.4.40 Date.prototype.toLocaleTimeString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a String value. The contents of the String are
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.4.4.41 Date.prototype.toString ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let tv be dateObject.[[DateValue]].
- Return
ToDateString (tv).
For any Date d such that
d.[[DateValue]] is evenly divisible by 1000,
the result of Date.parse(d.toString()) = d.valueOf(). See
This method is not generic; it throws a
21.4.4.41.1 TimeString ( tv )
The abstract operation TimeString takes argument tv (a Number, but not
- Let hour be
ToZeroPaddedDecimalString (ℝ (HourFromTime (tv)), 2). - Let minute be
ToZeroPaddedDecimalString (ℝ (MinFromTime (tv)), 2). - Let second be
ToZeroPaddedDecimalString (ℝ (SecFromTime (tv)), 2). - Return the
string-concatenation of hour,":" , minute,":" , second, the code unit 0x0020 (SPACE), and"GMT" .
21.4.4.41.2 DateString ( tv )
The abstract operation DateString takes argument tv (a Number, but not
- Let weekday be the Name of the entry in
Table 65 with the NumberWeekDay (tv). - Let month be the Name of the entry in
Table 66 with the NumberMonthFromTime (tv). - Let day be
ToZeroPaddedDecimalString (ℝ (DateFromTime (tv)), 2). - Let yv be
YearFromTime (tv). - If yv is
+0 𝔽 or yv >+0 𝔽, let yearSign be the empty String; otherwise let yearSign be"-" . - Let paddedYear be
ToZeroPaddedDecimalString (abs (ℝ (yv)), 4). - Return the
string-concatenation of weekday, the code unit 0x0020 (SPACE), month, the code unit 0x0020 (SPACE), day, the code unit 0x0020 (SPACE), yearSign, and paddedYear.
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21.4.4.41.3 TimeZoneString ( tv )
The abstract operation TimeZoneString takes argument tv (an
- Let systemTimeZoneIdentifier be
SystemTimeZoneIdentifier (). - If
IsTimeZoneOffsetString (systemTimeZoneIdentifier) istrue , then- Let offsetNs be
ParseTimeZoneOffsetString (systemTimeZoneIdentifier).
- Let offsetNs be
- Else,
- Let offsetNs be
GetNamedTimeZoneOffsetNanoseconds (systemTimeZoneIdentifier,ℤ (ℝ (tv) × 106)).
- Let offsetNs be
- Let offset be
𝔽 (truncate (offsetNs / 106)). - If offset is
+0 𝔽 or offset >+0 𝔽, then- Let offsetSign be
"+" . - Let absOffset be offset.
- Let offsetSign be
- Else,
- Let offsetSign be
"-" . - Let absOffset be -offset.
- Let offsetSign be
- Let offsetMin be
ToZeroPaddedDecimalString (ℝ (MinFromTime (absOffset)), 2). - Let offsetHour be
ToZeroPaddedDecimalString (ℝ (HourFromTime (absOffset)), 2). - Let tzName be an
implementation-defined string that is either the empty String or thestring-concatenation of the code unit 0x0020 (SPACE), the code unit 0x0028 (LEFT PARENTHESIS), animplementation-defined timezone name, and the code unit 0x0029 (RIGHT PARENTHESIS). - Return the
string-concatenation of offsetSign, offsetHour, offsetMin, and tzName.
21.4.4.41.4 ToDateString ( tv )
The abstract operation ToDateString takes argument tv (an
- If tv is
NaN , return"Invalid Date" . - Let t be
LocalTime (tv). - Return the
string-concatenation ofDateString (t), the code unit 0x0020 (SPACE),TimeString (t), andTimeZoneString (tv).
21.4.4.42 Date.prototype.toTimeString ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let tv be dateObject.[[DateValue]].
- If tv is
NaN , return"Invalid Date" . - Let t be
LocalTime (tv). - Return the
string-concatenation ofTimeString (t) andTimeZoneString (tv).
21.4.4.43 Date.prototype.toUTCString ( )
This method returns a String value representing the instant in time corresponding to the
It performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let tv be dateObject.[[DateValue]].
- If tv is
NaN , return"Invalid Date" . - Let weekday be the Name of the entry in
Table 65 with the NumberWeekDay (tv). - Let month be the Name of the entry in
Table 66 with the NumberMonthFromTime (tv). - Let day be
ToZeroPaddedDecimalString (ℝ (DateFromTime (tv)), 2). - Let yv be
YearFromTime (tv). - If yv is
+0 𝔽 or yv >+0 𝔽, let yearSign be the empty String; otherwise let yearSign be"-" . - Let paddedYear be
ToZeroPaddedDecimalString (abs (ℝ (yv)), 4). - Return the
string-concatenation of weekday,"," , the code unit 0x0020 (SPACE), day, the code unit 0x0020 (SPACE), month, the code unit 0x0020 (SPACE), yearSign, paddedYear, the code unit 0x0020 (SPACE), andTimeString (tv).
21.4.4.44 Date.prototype.valueOf ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Return dateObject.[[DateValue]].
21.4.4.45 Date.prototype [ %Symbol.toPrimitive% ] ( hint )
This method is called by ECMAScript language operators to convert a Date to a primitive
value. The allowed values for hint are
It performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - If hint is either
"string" or"default" , then- Let tryFirst be
string .
- Let tryFirst be
- Else if hint is
"number" , then- Let tryFirst be
number .
- Let tryFirst be
- Else,
- Throw a
TypeError exception.
- Throw a
- Return ?
OrdinaryToPrimitive (O, tryFirst).
This property has the attributes { [[Writable]]:
The value of the
21.4.5 Properties of Date Instances
Date instances are
22 Text Processing
22.1 String Objects
22.1.1 The String Constructor
The String
- is %String%.
- is the initial value of the
"String" property of theglobal object . - creates and initializes a new String object when called as a
constructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified String behaviour must include asupercall to the Stringconstructor to create and initialize the subclass instance with a [[StringData]] internal slot.
22.1.1.1 String ( value )
This function performs the following steps when called:
- If value is not present, then
- Let s be the empty String.
- Else,
- If NewTarget is
undefined and valueis a Symbol , returnSymbolDescriptiveString (value). - Let s be ?
ToString (value).
- If NewTarget is
- If NewTarget is
undefined , return s. - Return
StringCreate (s, ?GetPrototypeFromConstructor (NewTarget,"%String.prototype%" )).
22.1.2 Properties of the String Constructor
The String
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
22.1.2.1 String.fromCharCode ( ...codeUnits )
This function may be called with any number of arguments which form the rest parameter codeUnits.
It performs the following steps when called:
- Let result be the empty String.
- For each element next of codeUnits, do
- Let nextCU be the code unit whose numeric value is
ℝ (?ToUint16 (next)). - Set result to the
string-concatenation of result and nextCU.
- Let nextCU be the code unit whose numeric value is
- Return result.
The
22.1.2.2 String.fromCodePoint ( ...codePoints )
This function may be called with any number of arguments which form the rest parameter codePoints.
It performs the following steps when called:
- Let result be the empty String.
- For each element next of codePoints, do
- Let nextCP be ?
ToNumber (next). - If nextCP is not an
integral Number , throw aRangeError exception. - If
ℝ (nextCP) < 0 orℝ (nextCP) > 0x10FFFF, throw aRangeError exception. - Set result to the
string-concatenation of result andUTF16EncodeCodePoint (ℝ (nextCP)).
- Let nextCP be ?
Assert : If codePoints is empty, then result is the empty String.- Return result.
The
22.1.2.3 String.prototype
The initial value of String.prototype is the
This property has the attributes { [[Writable]]:
22.1.2.4 String.raw ( template, ...substitutions )
This function may be called with a variable number of arguments. The first argument is
template and the remainder of the arguments form the
It performs the following steps when called:
- Let substitutionCount be the number of elements in substitutions.
- Let cooked be ?
ToObject (template). - Let literals be ?
ToObject (?Get (cooked,"raw" )). - Let literalCount be ?
LengthOfArrayLike (literals). - If literalCount ≤ 0, return the empty String.
- Let R be the empty String.
- Let nextIndex be 0.
- Repeat,
- Let nextLiteralVal be ?
Get (literals, !ToString (𝔽 (nextIndex))). - Let nextLiteral be ?
ToString (nextLiteralVal). - Set R to the
string-concatenation of R and nextLiteral. - If nextIndex + 1 = literalCount, return R.
- If nextIndex < substitutionCount, then
- Let nextSubVal be substitutions[nextIndex].
- Let nextSub be ?
ToString (nextSubVal). - Set R to the
string-concatenation of R and nextSub.
- Set nextIndex to nextIndex + 1.
- Let nextLiteralVal be ?
This function is intended for use as a tag function of a Tagged Template (
22.1.3 Properties of the String Prototype Object
The String prototype object:
- is %String.prototype%.
is a String exotic object and has the internal methods specified for such objects.- has a [[StringData]] internal slot whose value is the empty String.
- has a
"length" property whose initial value is+0 𝔽 and whose attributes are { [[Writable]]:false , [[Enumerable]]:false , [[Configurable]]:false }. - has a [[Prototype]] internal slot whose value is
%Object.prototype% .
Unless explicitly stated otherwise, the methods of the String prototype object defined below are
not generic and the
22.1.3.1 String.prototype.at ( index )
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let len be the length of S.
- Let relativeIndex be ?
ToIntegerOrInfinity (index). - If relativeIndex ≥ 0, then
- Let k be relativeIndex.
- Else,
- Let k be len + relativeIndex.
- If k < 0 or k ≥ len, return
undefined . - Return the
substring of S from k to k + 1.
22.1.3.2 String.prototype.charAt ( pos )
This method returns a single element String containing the code unit at index
pos within the String value resulting from converting this object to a
String. If there is no element at that index, the result is the empty String. The
result
If pos is an x.charAt(pos) is equivalent to the result of
x.substring(pos, pos + 1).
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let position be ?
ToIntegerOrInfinity (pos). - Let size be the length of S.
- If position < 0 or position ≥ size, return the empty String.
- Return the
substring of S from position to position + 1.
This method is intentionally generic; it does not require that its
22.1.3.3 String.prototype.charCodeAt ( pos )
This method returns a Number (a non-negative
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let position be ?
ToIntegerOrInfinity (pos). - Let size be the length of S.
- If position < 0 or position ≥ size, return
NaN . - Return the
Number value for the numeric value of the code unit at index position within the String S.
This method is intentionally generic; it does not require that its
22.1.3.4 String.prototype.codePointAt ( pos )
This method returns a non-negative
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let position be ?
ToIntegerOrInfinity (pos). - Let size be the length of S.
- If position < 0 or position ≥ size, return
undefined . - Let cp be
CodePointAt (S, position). - Return
𝔽 (cp.[[CodePoint]]).
This method is intentionally generic; it does not require that its
22.1.3.5 String.prototype.concat ( ...args )
When this method is called it returns the String value consisting of the code units
of the
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let R be S.
- For each element next of args, do
- Let nextString be ?
ToString (next). - Set R to the
string-concatenation of R and nextString.
- Let nextString be ?
- Return R.
The
This method is intentionally generic; it does not require that its
22.1.3.6 String.prototype.constructor
The initial value of String.prototype.constructor is
22.1.3.7 String.prototype.endsWith ( searchString [ , endPosition ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let isRegExp be ?
IsRegExp (searchString). - If isRegExp is
true , throw aTypeError exception. - Let searchStr be ?
ToString (searchString). - Let len be the length of S.
- If endPosition is
undefined , let pos be len; else let pos be ?ToIntegerOrInfinity (endPosition). - Let end be the result of
clamping pos between 0 and len. - Let searchLength be the length of searchStr.
- If searchLength = 0, return
true . - Let start be end - searchLength.
- If start < 0, return
false . - Let substring be the
substring of S from start to end. - If substring is searchStr, return
true . - Return
false .
This method returns
Throwing an exception if the first argument is a RegExp is specified in order to allow future editions to define extensions that allow such argument values.
This method is intentionally generic; it does not require that its
22.1.3.8 String.prototype.includes ( searchString [ , position ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let isRegExp be ?
IsRegExp (searchString). - If isRegExp is
true , throw aTypeError exception. - Let searchStr be ?
ToString (searchString). - Let pos be ?
ToIntegerOrInfinity (position). Assert : If position isundefined , then pos is 0.- Let len be the length of S.
- Let start be the result of
clamping pos between 0 and len. - Let index be
StringIndexOf (S, searchStr, start). - If index is
not-found , returnfalse . - Return
true .
If searchString appears as a
Throwing an exception if the first argument is a RegExp is specified in order to allow future editions to define extensions that allow such argument values.
This method is intentionally generic; it does not require that its
22.1.3.9 String.prototype.indexOf ( searchString [ , position ] )
If searchString appears as a
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let searchStr be ?
ToString (searchString). - Let pos be ?
ToIntegerOrInfinity (position). Assert : If position isundefined , then pos is 0.- Let len be the length of S.
- Let start be the result of
clamping pos between 0 and len. - Let result be
StringIndexOf (S, searchStr, start). - If result is
not-found , return-1 𝔽. - Return
𝔽 (result).
This method is intentionally generic; it does not require that its
22.1.3.10 String.prototype.isWellFormed ( )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Return
IsStringWellFormedUnicode (S).
22.1.3.11 String.prototype.lastIndexOf ( searchString [ , position ] )
If searchString appears as a
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let searchStr be ?
ToString (searchString). - Let numPos be ?
ToNumber (position). Assert : If position isundefined , then numPos isNaN .- If numPos is
NaN , let pos be +∞; otherwise let pos be !ToIntegerOrInfinity (numPos). - Let len be the length of S.
- Let searchLen be the length of searchStr.
- Let start be the result of
clamping pos between 0 and len - searchLen. - Let result be
StringLastIndexOf (S, searchStr, start). - If result is
not-found , return-1 𝔽. - Return
𝔽 (result).
This method is intentionally generic; it does not require that its
22.1.3.12 String.prototype.localeCompare ( that [ , reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a Number other than
Before performing the comparisons, this method performs the following steps to prepare the Strings:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let thatValue be ?
ToString (that).
The meaning of the optional second and third parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not assign any other interpretation to those parameter positions.
The actual return values are
This method itself is not directly suitable as an argument to
Array.prototype.sort because the latter requires a function of two
arguments.
This method may rely on whatever language- and/or locale-sensitive comparison
functionality is available to the ECMAScript environment from the
// Å ANGSTROM SIGN vs.
// Å LATIN CAPITAL LETTER A + COMBINING RING ABOVE
"\u212B".localeCompare("A\u030A")
// Ω OHM SIGN vs.
// Ω GREEK CAPITAL LETTER OMEGA
"\u2126".localeCompare("\u03A9")
// ṩ LATIN SMALL LETTER S WITH DOT BELOW AND DOT ABOVE vs.
// ṩ LATIN SMALL LETTER S + COMBINING DOT ABOVE + COMBINING DOT BELOW
"\u1E69".localeCompare("s\u0307\u0323")
// ḍ̇ LATIN SMALL LETTER D WITH DOT ABOVE + COMBINING DOT BELOW vs.
// ḍ̇ LATIN SMALL LETTER D WITH DOT BELOW + COMBINING DOT ABOVE
"\u1E0B\u0323".localeCompare("\u1E0D\u0307")
// 가 HANGUL CHOSEONG KIYEOK + HANGUL JUNGSEONG A vs.
// 가 HANGUL SYLLABLE GA
"\u1100\u1161".localeCompare("\uAC00")For a definition and discussion of canonical equivalence see the Unicode Standard, chapters 2 and 3, as well as Unicode Standard Annex #15, Unicode Normalization Forms and Unicode Technical Note #5, Canonical Equivalence in Applications. Also see Unicode Technical Standard #10, Unicode Collation Algorithm.
It is recommended that this method should not honour Unicode compatibility equivalents or compatibility decompositions as defined in the Unicode Standard, chapter 3, section 3.7.
This method is intentionally generic; it does not require that its
22.1.3.13 String.prototype.match ( regexp )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If regexp is neither
undefined nornull , then- Let matcher be ?
GetMethod (regexp,%Symbol.match% ). - If matcher is not
undefined , then- Return ?
Call (matcher, regexp, « O »).
- Return ?
- Let matcher be ?
- Let S be ?
ToString (O). - Let rx be ?
RegExpCreate (regexp,undefined ). - Return ?
Invoke (rx,%Symbol.match% , « S »).
This method is intentionally generic; it does not require that its
22.1.3.14 String.prototype.matchAll ( regexp )
This method performs a regular expression match of the String representing the
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If regexp is neither
undefined nornull , then- Let isRegExp be ?
IsRegExp (regexp). - If isRegExp is
true , then- Let flags be ?
Get (regexp,"flags" ). - Perform ?
RequireObjectCoercible (flags). - If ?
ToString (flags) does not contain"g" , throw aTypeError exception.
- Let flags be ?
- Let matcher be ?
GetMethod (regexp,%Symbol.matchAll% ). - If matcher is not
undefined , then- Return ?
Call (matcher, regexp, « O »).
- Return ?
- Let isRegExp be ?
- Let S be ?
ToString (O). - Let rx be ?
RegExpCreate (regexp,"g" ). - Return ?
Invoke (rx,%Symbol.matchAll% , « S »).
String.prototype.split,
String.prototype.matchAll is designed to typically act without mutating its
inputs.
22.1.3.15 String.prototype.normalize ( [ form ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - If form is
undefined , let f be"NFC" . - Else, let f be ?
ToString (form). - If f is not one of
"NFC" ,"NFD" ,"NFKC" , or"NFKD" , throw aRangeError exception. - Let ns be the String value that is the result of normalizing S into the normalization form named by f as specified in the latest Unicode Standard, Normalization Forms.
- Return ns.
This method is intentionally generic; it does not require that its
22.1.3.16 String.prototype.padEnd ( maxLength [ , fillString ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Return ?
StringPaddingBuiltinsImpl (O, maxLength, fillString,end ).
22.1.3.17 String.prototype.padStart ( maxLength [ , fillString ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Return ?
StringPaddingBuiltinsImpl (O, maxLength, fillString,start ).
22.1.3.17.1 StringPaddingBuiltinsImpl ( O, maxLength, fillString, placement )
The abstract operation StringPaddingBuiltinsImpl takes arguments O (an
- Let S be ?
ToString (O). - Let intMaxLength be
ℝ (?ToLength (maxLength)). - Let stringLength be the length of S.
- If intMaxLength ≤ stringLength, return S.
- If fillString is
undefined , set fillString to the String value consisting solely of the code unit 0x0020 (SPACE). - Else, set fillString to ?
ToString (fillString). - Return
StringPad (S, intMaxLength, fillString, placement).
22.1.3.17.2 StringPad ( S, maxLength, fillString, placement )
The abstract operation StringPad takes arguments S (a String),
maxLength (a non-negative
- Let stringLength be the length of S.
- If maxLength ≤ stringLength, return S.
- If fillString is the empty String, return S.
- Let fillLen be maxLength - stringLength.
- Let truncatedStringFiller be the String value consisting of repeated concatenations of fillString truncated to length fillLen.
- If placement is
start , return thestring-concatenation of truncatedStringFiller and S. - Else, return the
string-concatenation of S and truncatedStringFiller.
The argument maxLength will be clamped such that it can be no smaller than the length of S.
The argument fillString defaults to
22.1.3.17.3 ToZeroPaddedDecimalString ( n, minLength )
The abstract operation ToZeroPaddedDecimalString takes arguments n (a
non-negative
- Let S be the String representation of n, formatted as a decimal number.
- Return
StringPad (S, minLength,"0" ,start ).
22.1.3.18 String.prototype.repeat ( count )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let n be ?
ToIntegerOrInfinity (count). - If n < 0 or n = +∞, throw a
RangeError exception. - If n = 0, return the empty String.
- Return the String value that is made from n copies of S appended together.
This method creates the String value consisting of the code units of the
This method is intentionally generic; it does not require that its
22.1.3.19 String.prototype.replace ( searchValue, replaceValue )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If searchValue is neither
undefined nornull , then- Let replacer be ?
GetMethod (searchValue,%Symbol.replace% ). - If replacer is not
undefined , then- Return ?
Call (replacer, searchValue, « O, replaceValue »).
- Return ?
- Let replacer be ?
- Let string be ?
ToString (O). - Let searchString be ?
ToString (searchValue). - Let functionalReplace be
IsCallable (replaceValue). - If functionalReplace is
false , then- Set replaceValue to ?
ToString (replaceValue).
- Set replaceValue to ?
- Let searchLength be the length of searchString.
- Let position be
StringIndexOf (string, searchString, 0). - If position is
not-found , return string. - Let preceding be the
substring of string from 0 to position. - Let following be the
substring of string from position + searchLength. - If functionalReplace is
true , then - Else,
Assert : replaceValueis a String .- Let captures be a new empty
List . - Let replacement be !
GetSubstitution (searchString, string, position, captures,undefined , replaceValue).
- Return the
string-concatenation of preceding, replacement, and following.
This method is intentionally generic; it does not require that its
22.1.3.19.1 GetSubstitution ( matched, str, position, captures, namedCaptures, replacementTemplate )
The abstract operation GetSubstitution takes arguments matched (a String),
str (a String), position (a non-negative
- Let stringLength be the length of str.
Assert : position ≤ stringLength.- Let result be the empty String.
- Let templateRemainder be replacementTemplate.
- Repeat, while templateRemainder is not the empty String,
- NOTE: The following steps isolate ref (a prefix of templateRemainder), determine refReplacement (its replacement), and then append that replacement to result.
- If templateRemainder starts with
"$$" , then- Let ref be
"$$" . - Let refReplacement be
"$" .
- Let ref be
- Else if templateRemainder starts with
"$`" , then- Let ref be
"$`" . - Let refReplacement be the
substring of str from 0 to position.
- Let ref be
- Else if templateRemainder starts with
"$&" , then- Let ref be
"$&" . - Let refReplacement be matched.
- Let ref be
- Else if templateRemainder starts with
"$'" (0x0024 (DOLLAR SIGN) followed by 0x0027 (APOSTROPHE)), then- Let ref be
"$'" . - Let matchLength be the length of matched.
- Let tailPos be position + matchLength.
- Let refReplacement be the
substring of str frommin (tailPos, stringLength). - NOTE: tailPos can exceed stringLength only
if this abstract operation was invoked by a call to the
intrinsic
%Symbol.replace% method of%RegExp.prototype% on an object whose"exec" property is not the intrinsic %RegExp.prototype.exec%.
- Let ref be
- Else if templateRemainder starts with
"$" followed by 1 or more decimal digits, then- If templateRemainder starts with
"$" followed by 2 or more decimal digits, let digitCount be 2; otherwise let digitCount be 1. - Let digits be the
substring of templateRemainder from 1 to 1 + digitCount. - Let index be
ℝ (StringToNumber (digits)). Assert : 0 ≤ index ≤ 99.- Let captureLen be the number of elements in captures.
- If index > captureLen and
digitCount = 2, then
- NOTE: When a two-digit replacement pattern specifies an index exceeding the count of capturing groups, it is treated as a one-digit replacement pattern followed by a literal digit.
- Set digitCount to 1.
- Set digits to the
substring of digits from 0 to 1. - Set index to
ℝ (StringToNumber (digits)).
- Let ref be the
substring of templateRemainder from 0 to 1 + digitCount. - If 1 ≤ index ≤ captureLen, then
- Let capture be captures[index - 1].
- If capture is
undefined , then- Let refReplacement be the empty String.
- Else,
- Let refReplacement be capture.
- Else,
- Let refReplacement be ref.
- If templateRemainder starts with
- Else if templateRemainder starts with
"$<" , then- Let gtPos be
StringIndexOf (templateRemainder,">" , 0). - If gtPos is
not-found or namedCaptures isundefined , then- Let ref be
"$<" . - Let refReplacement be ref.
- Let ref be
- Else,
- Let ref be the
substring of templateRemainder from 0 to gtPos + 1. - Let groupName be the
substring of templateRemainder from 2 to gtPos. Assert : namedCapturesis an Object .- Let capture be ?
Get (namedCaptures, groupName). - If capture is
undefined , then- Let refReplacement be the empty String.
- Else,
- Let refReplacement be
?
ToString (capture).
- Let refReplacement be
?
- Let ref be the
- Let gtPos be
- Else,
- Let ref be the
substring of templateRemainder from 0 to 1. - Let refReplacement be ref.
- Let ref be the
- Let refLength be the length of ref.
- Set templateRemainder to the
substring of templateRemainder from refLength. - Set result to the
string-concatenation of result and refReplacement.
- Return result.
22.1.3.20 String.prototype.replaceAll ( searchValue, replaceValue )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If searchValue is neither
undefined nornull , then- Let isRegExp be ?
IsRegExp (searchValue). - If isRegExp is
true , then- Let flags be ?
Get (searchValue,"flags" ). - Perform ?
RequireObjectCoercible (flags). - If ?
ToString (flags) does not contain"g" , throw aTypeError exception.
- Let flags be ?
- Let replacer be ?
GetMethod (searchValue,%Symbol.replace% ). - If replacer is not
undefined , then- Return ?
Call (replacer, searchValue, « O, replaceValue »).
- Return ?
- Let isRegExp be ?
- Let string be ?
ToString (O). - Let searchString be ?
ToString (searchValue). - Let functionalReplace be
IsCallable (replaceValue). - If functionalReplace is
false , then- Set replaceValue to ?
ToString (replaceValue).
- Set replaceValue to ?
- Let searchLength be the length of searchString.
- Let advanceBy be
max (1, searchLength). - Let matchPositions be a new empty
List . - Let position be
StringIndexOf (string, searchString, 0). - Repeat, while position is not
not-found ,- Append position to matchPositions.
- Set position to
StringIndexOf (string, searchString, position + advanceBy).
- Let endOfLastMatch be 0.
- Let result be the empty String.
- For each element p of matchPositions, do
- Let preserved be the
substring of string from endOfLastMatch to p. - If functionalReplace is
true , then - Else,
Assert : replaceValueis a String .- Let captures be a new empty
List . - Let replacement be !
GetSubstitution (searchString, string, p, captures,undefined , replaceValue).
- Set result to the
string-concatenation of result, preserved, and replacement. - Set endOfLastMatch to p + searchLength.
- Let preserved be the
- If endOfLastMatch < the length of string, then
- Set result to the
string-concatenation of result and thesubstring of string from endOfLastMatch.
- Set result to the
- Return result.
22.1.3.21 String.prototype.search ( regexp )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If regexp is neither
undefined nornull , then- Let searcher be ?
GetMethod (regexp,%Symbol.search% ). - If searcher is not
undefined , then- Return ?
Call (searcher, regexp, « O »).
- Return ?
- Let searcher be ?
- Let string be ?
ToString (O). - Let rx be ?
RegExpCreate (regexp,undefined ). - Return ?
Invoke (rx,%Symbol.search% , « string »).
This method is intentionally generic; it does not require that its
22.1.3.22 String.prototype.slice ( start, end )
This method returns a
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let len be the length of S.
- Let intStart be ?
ToIntegerOrInfinity (start). - If intStart = -∞, let from be 0.
- Else if intStart < 0, let from be
max (len + intStart, 0). - Else, let from be
min (intStart, len). - If end is
undefined , let intEnd be len; else let intEnd be ?ToIntegerOrInfinity (end). - If intEnd = -∞, let to be 0.
- Else if intEnd < 0, let to be
max (len + intEnd, 0). - Else, let to be
min (intEnd, len). - If from ≥ to, return the empty String.
- Return the
substring of S from from to to.
This method is intentionally generic; it does not require that its
22.1.3.23 String.prototype.split ( separator, limit )
This method returns an Array into which substrings of the result of converting this object to
a String have been stored. The substrings are determined by searching from left to right for
occurrences of separator; these occurrences are not part of any String in the
returned array, but serve to divide up the String value. The value of separator
may be a String of any length or it may be an object, such as a RegExp, that has a
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If separator is neither
undefined nornull , then- Let splitter be ?
GetMethod (separator,%Symbol.split% ). - If splitter is not
undefined , then- Return ?
Call (splitter, separator, « O, limit »).
- Return ?
- Let splitter be ?
- Let S be ?
ToString (O). - If limit is
undefined , let lim be 232 - 1; else let lim beℝ (?ToUint32 (limit)). - Let R be ?
ToString (separator). - If lim = 0, then
- Return
CreateArrayFromList (« »).
- Return
- If separator is
undefined , then- Return
CreateArrayFromList (« S »).
- Return
- Let separatorLength be the length of R.
- If separatorLength = 0, then
- Let strLen be the length of S.
- Let outLen be the result of
clamping lim between 0 and strLen. - Let head be the
substring of S from 0 to outLen. - Let codeUnits be a
List consisting of the sequence of code units that are the elements of head. - Return
CreateArrayFromList (codeUnits).
- If S is the empty String, return
CreateArrayFromList (« S »). - Let substrings be a new empty
List . - Let i be 0.
- Let j be
StringIndexOf (S, R, 0). - Repeat, while j is not
not-found ,- Let T be the
substring of S from i to j. - Append T to substrings.
- If the number of elements in substrings is lim, return
CreateArrayFromList (substrings). - Set i to j + separatorLength.
- Set j to
StringIndexOf (S, R, i).
- Let T be the
- Let T be the
substring of S from i. - Append T to substrings.
- Return
CreateArrayFromList (substrings).
The value of separator may be an empty String. In this case,
separator does not match the empty
If the
If separator is
This method is intentionally generic; it does not require that its
22.1.3.24 String.prototype.startsWith ( searchString [ , position ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let isRegExp be ?
IsRegExp (searchString). - If isRegExp is
true , throw aTypeError exception. - Let searchStr be ?
ToString (searchString). - Let len be the length of S.
- If position is
undefined , let pos be 0; else let pos be ?ToIntegerOrInfinity (position). - Let start be the result of
clamping pos between 0 and len. - Let searchLength be the length of searchStr.
- If searchLength = 0, return
true . - Let end be start + searchLength.
- If end > len, return
false . - Let substring be the
substring of S from start to end. - If substring is searchStr, return
true . - Return
false .
This method returns
Throwing an exception if the first argument is a RegExp is specified in order to allow future editions to define extensions that allow such argument values.
This method is intentionally generic; it does not require that its
22.1.3.25 String.prototype.substring ( start, end )
This method returns a
If either argument is
If start is strictly greater than end, they are swapped.
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let len be the length of S.
- Let intStart be ?
ToIntegerOrInfinity (start). - If end is
undefined , let intEnd be len; else let intEnd be ?ToIntegerOrInfinity (end). - Let finalStart be the result of
clamping intStart between 0 and len. - Let finalEnd be the result of
clamping intEnd between 0 and len. - Let from be
min (finalStart, finalEnd). - Let to be
max (finalStart, finalEnd). - Return the
substring of S from from to to.
This method is intentionally generic; it does not require that its
22.1.3.26 String.prototype.toLocaleLowerCase ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method interprets a String value as a sequence of UTF-16 encoded code points, as
described in
It works exactly the same as toLowerCase except that it is intended to yield a
locale-sensitive result corresponding with conventions of the
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
This method is intentionally generic; it does not require that its
22.1.3.27 String.prototype.toLocaleUpperCase ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method interprets a String value as a sequence of UTF-16 encoded code points, as
described in
It works exactly the same as toUpperCase except that it is intended to yield a
locale-sensitive result corresponding with conventions of the
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
This method is intentionally generic; it does not require that its
22.1.3.28 String.prototype.toLowerCase ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as
described in
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let sText be
StringToCodePoints (S). - Let lowerText be toLowercase(sText), according to the Unicode Default Case Conversion algorithm.
- Let L be
CodePointsToString (lowerText). - Return L.
The result must be derived according to the locale-insensitive case mappings in the Unicode
Character Database (this explicitly includes not only the file UnicodeData.txt,
but also all locale-insensitive mappings in the file SpecialCasing.txt
that accompanies it).
The case mapping of some code points may produce multiple code points. In this case
the result String may not be the same length as the source String. Because both
toUpperCase and toLowerCase have context-sensitive
behaviour, the methods are not symmetrical. In other words,
s.toUpperCase().toLowerCase() is not necessarily equal to
s.toLowerCase().
This method is intentionally generic; it does not require that its
22.1.3.29 String.prototype.toString ( )
This method performs the following steps when called:
- Return ?
ThisStringValue (this value).
For a String object, this method happens to return the same thing as the
valueOf method.
22.1.3.30 String.prototype.toUpperCase ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as
described in
It behaves in exactly the same way as String.prototype.toLowerCase, except that
the String is mapped using the toUppercase algorithm of the Unicode Default Case Conversion.
This method is intentionally generic; it does not require that its
22.1.3.31 String.prototype.toWellFormed ( )
This method returns a String representation of this object with all
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let strLen be the length of S.
- Let k be 0.
- Let result be the empty String.
- Repeat, while k < strLen,
- Let cp be
CodePointAt (S, k). - If cp.[[IsUnpairedSurrogate]] is
true , then- Set result to the
string-concatenation of result and 0xFFFD (REPLACEMENT CHARACTER).
- Set result to the
- Else,
- Set result to the
string-concatenation of result andUTF16EncodeCodePoint (cp.[[CodePoint]]).
- Set result to the
- Set k to k + cp.[[CodeUnitCount]].
- Let cp be
- Return result.
22.1.3.32 String.prototype.trim ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as
described in
It performs the following steps when called:
- Let S be the
this value. - Return ?
TrimString (S,start+end ).
This method is intentionally generic; it does not require that its
22.1.3.32.1 TrimString ( string, where )
The abstract operation TrimString takes arguments string (an
- Let str be ?
RequireObjectCoercible (string). - Let S be ?
ToString (str). - If where is
start , then- Let T be the String value that is a copy of S with leading white space removed.
- Else if where is
end , then- Let T be the String value that is a copy of S with trailing white space removed.
- Else,
Assert : where isstart+end .- Let T be the String value that is a copy of S with both leading and trailing white space removed.
- Return T.
The definition of white space is the union of
22.1.3.33 String.prototype.trimEnd ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as
described in
It performs the following steps when called:
- Let S be the
this value. - Return ?
TrimString (S,end ).
This method is intentionally generic; it does not require that its
22.1.3.34 String.prototype.trimStart ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as
described in
It performs the following steps when called:
- Let S be the
this value. - Return ?
TrimString (S,start ).
This method is intentionally generic; it does not require that its
22.1.3.35 String.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ThisStringValue (this value).
22.1.3.35.1 ThisStringValue ( value )
The abstract operation ThisStringValue takes argument value (an
- If value
is a String , return value. - If value
is an Object and value has a [[StringData]] internal slot, then- Let s be value.[[StringData]].
Assert : sis a String .- Return s.
- Throw a
TypeError exception.
22.1.3.36 String.prototype [ %Symbol.iterator% ] ( )
This method returns an
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let s be ?
ToString (O). - Let closure be a new
Abstract Closure with no parameters that captures s and performs the following steps when called:- Let len be the length of s.
- Let position be 0.
- Repeat, while position < len,
- Let cp be
CodePointAt (s, position). - Let nextIndex be position + cp.[[CodeUnitCount]].
- Let resultString be the
substring of s from position to nextIndex. - Set position to nextIndex.
- Perform ?
GeneratorYield (CreateIteratorResultObject (resultString,false )).
- Let cp be
- Return
NormalCompletion (unused ).
- Return
CreateIteratorFromClosure (closure,"%StringIteratorPrototype%" ,%StringIteratorPrototype% ).
The value of the
22.1.4 Properties of String Instances
String instances are
String instances have a
22.1.4.1 length
The number of elements in the String value represented by this String object.
Once a String object is initialized, this property is unchanging. It has the attributes {
[[Writable]]:
22.1.5 String Iterator Objects
A String Iterator is an object that represents a specific iteration over
some specific String instance object. There is not a named
22.1.5.1 The %StringIteratorPrototype% Object
The %StringIteratorPrototype% object:
- has properties that are inherited by all
String Iterator objects . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Iterator.prototype% . - has the following properties:
22.1.5.1.1 %StringIteratorPrototype%.next ( )
- Return ?
GeneratorResume (this value,empty ,"%StringIteratorPrototype%" ).
22.1.5.1.2 %StringIteratorPrototype% [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
22.2 RegExp (Regular Expression) Objects
A RegExp object contains a regular expression and the associated flags.
The form and functionality of regular expressions is modelled after the regular expression facility in the Perl 5 programming language.
22.2.1 Patterns
The RegExp
Syntax
Each \u u u \u
The first two lines here are equivalent to CharacterClass.
A number of productions in this section are given alternative definitions in section
22.2.1.1 Static Semantics: Early Errors
This section is amended in
-
It is a Syntax Error if
CountLeftCapturingParensWithin (Pattern ) ≥ 232 - 1. -
It is a Syntax Error if
Pattern contains two distinctGroupSpecifier s x and y such that theCapturingGroupName of x is theCapturingGroupName of y and such thatMightBothParticipate (x, y) istrue .
-
It is a Syntax Error if the MV of the first
DecimalDigits is strictly greater than the MV of the secondDecimalDigits .
-
It is a Syntax Error if the
source text matched by RegularExpressionModifiers contains the same code point more than once.
-
It is a Syntax Error if the
source text matched by the firstRegularExpressionModifiers and thesource text matched by the secondRegularExpressionModifiers are both empty. -
It is a Syntax Error if the
source text matched by the firstRegularExpressionModifiers contains the same code point more than once. -
It is a Syntax Error if the
source text matched by the secondRegularExpressionModifiers contains the same code point more than once. -
It is a Syntax Error if any code point in the
source text matched by the firstRegularExpressionModifiers is also contained in thesource text matched by the secondRegularExpressionModifiers .
-
It is a Syntax Error if
GroupSpecifiersThatMatch (GroupName ) is empty.
-
It is a Syntax Error if the
CapturingGroupNumber ofDecimalEscape is strictly greater thanCountLeftCapturingParensWithin (thePattern containingAtomEscape ).
-
It is a Syntax Error if
IsCharacterClass of the firstClassAtom istrue orIsCharacterClass of the secondClassAtom istrue . -
It is a Syntax Error if
IsCharacterClass of the firstClassAtom isfalse ,IsCharacterClass of the secondClassAtom isfalse , and theCharacterValue of the firstClassAtom is strictly greater than theCharacterValue of the secondClassAtom .
-
It is a Syntax Error if
IsCharacterClass ofClassAtomNoDash istrue orIsCharacterClass ofClassAtom istrue . -
It is a Syntax Error if
IsCharacterClass ofClassAtomNoDash isfalse ,IsCharacterClass ofClassAtom isfalse , and theCharacterValue ofClassAtomNoDash is strictly greater than theCharacterValue ofClassAtom .
-
It is a Syntax Error if the
CharacterValue ofRegExpUnicodeEscapeSequence is not the numeric value of some code point matched by theIdentifierStartChar lexical grammar production.
-
It is a Syntax Error if the
RegExpIdentifierCodePoint ofRegExpIdentifierStart is not matched by theUnicodeIDStart lexical grammar production.
-
It is a Syntax Error if the
CharacterValue ofRegExpUnicodeEscapeSequence is not the numeric value of some code point matched by theIdentifierPartChar lexical grammar production.
-
It is a Syntax Error if the
RegExpIdentifierCodePoint ofRegExpIdentifierPart is not matched by theUnicodeIDContinue lexical grammar production.
-
It is a Syntax Error if the
source text matched by UnicodePropertyName is not a Unicodeproperty name or property alias listed in the “Property name and aliases” column ofTable 69 . -
It is a Syntax Error if the
source text matched by UnicodePropertyValue is not a property value or property value alias for the Unicode property or property alias given by thesource text matched by UnicodePropertyName listed inPropertyValueAliases.txt.
-
It is a Syntax Error if the
source text matched by LoneUnicodePropertyNameOrValue is not a Unicode property value or property value alias for the General_Category (gc) property listed inPropertyValueAliases.txt, nor a binary property or binary property alias listed in the “Property name and aliases” column ofTable 70 , nor a binary property of strings listed in the “Property name ” column ofTable 71 . -
It is a Syntax Error if the enclosing
Pattern does not have a [UnicodeSetsMode] parameter and thesource text matched by LoneUnicodePropertyNameOrValue is a binary property of strings listed in the “Property name ” column ofTable 71 .
-
It is a Syntax Error if
MayContainStrings of theUnicodePropertyValueExpression istrue .
-
It is a Syntax Error if
MayContainStrings of theClassContents istrue .
-
It is a Syntax Error if
MayContainStrings of theClassContents istrue .
-
It is a Syntax Error if the
CharacterValue of the firstClassSetCharacter is strictly greater than theCharacterValue of the secondClassSetCharacter .
22.2.1.2 Static Semantics: CountLeftCapturingParensWithin ( node )
The abstract operation CountLeftCapturingParensWithin takes argument node (a
( pattern character that is matched by the ( terminal of the
This section is amended in
It performs the following steps when called:
Assert : node is an instance of a production inthe RegExp Pattern grammar .- Return the number of
Atom :: ( GroupSpecifier opt Disjunction ) Parse Nodes contained within node.
22.2.1.3 Static Semantics: CountLeftCapturingParensBefore ( node )
The abstract operation CountLeftCapturingParensBefore takes argument node (a
This section is amended in
It performs the following steps when called:
Assert : node is an instance of a production inthe RegExp Pattern grammar .- Let pattern be the
Pattern containing node. - Return the number of
Atom :: ( GroupSpecifier opt Disjunction ) Parse Nodes contained within pattern that either occur before node or contain node.
22.2.1.4 Static Semantics: MightBothParticipate ( x, y )
The abstract operation MightBothParticipate takes arguments x (a
Assert : x and y have the same enclosingPattern .- If the enclosing
Pattern contains aDisjunction :: Alternative | Disjunction Parse Node such that either x is contained within theAlternative and y is contained within the derivedDisjunction , or x is contained within the derivedDisjunction and y is contained within theAlternative , returnfalse . - Return
true .
22.2.1.5 Static Semantics: CapturingGroupNumber
The
This section is amended in
It is defined piecewise over the following productions:
- Return the MV of
NonZeroDigit .
- Let n be the number of code points in
DecimalDigits . - Return (the MV of
NonZeroDigit × 10n plus the MV ofDecimalDigits ).
The definitions of “the MV of
22.2.1.6 Static Semantics: IsCharacterClass
The
This section is amended in
It is defined piecewise over the following productions:
- Return
false .
- Return
true .
22.2.1.7 Static Semantics: CharacterValue
The
This section is amended in
It is defined piecewise over the following productions:
- Return the numeric value of U+002D (HYPHEN-MINUS).
- Let ch be the code point matched by
SourceCharacter . - Return the numeric value of ch.
- Return the numeric value of U+0008 (BACKSPACE).
- Return the numeric value of U+002D (HYPHEN-MINUS).
- Return the numeric value according to
Table 67 .
| ControlEscape | Numeric Value | Code Point | Unicode Name | Symbol |
|---|---|---|---|---|
t
|
9 |
U+0009
|
CHARACTER TABULATION | <HT> |
n
|
10 |
U+000A
|
LINE FEED (LF) | <LF> |
v
|
11 |
U+000B
|
LINE TABULATION | <VT> |
f
|
12 |
U+000C
|
FORM FEED (FF) | <FF> |
r
|
13 |
U+000D
|
CARRIAGE RETURN (CR) | <CR> |
- Let ch be the code point matched by
AsciiLetter . - Let i be the numeric value of ch.
- Return the remainder of dividing i by 32.
- Return the numeric value of U+0000 (NULL).
\0 represents the <NUL> character and cannot be followed by a
decimal digit.
- Return the MV of
HexEscapeSequence .
- Let lead be the
CharacterValue ofHexLeadSurrogate . - Let trail be the
CharacterValue ofHexTrailSurrogate . - Let cp be
UTF16SurrogatePairToCodePoint (lead, trail). - Return the numeric value of cp.
- Return the MV of
Hex4Digits .
- Return the MV of
CodePoint .
- Return the MV of
Hex4Digits .
- Let ch be the code point matched by
IdentityEscape . - Return the numeric value of ch.
- Let ch be the code point matched by
SourceCharacter . - Return the numeric value of ch.
- Let ch be the code point matched by
ClassSetReservedPunctuator . - Return the numeric value of ch.
- Return the numeric value of U+0008 (BACKSPACE).
22.2.1.8 Static Semantics: MayContainStrings
The
- Return
false .
- If the
source text matched by LoneUnicodePropertyNameOrValue is a binary property of strings listed in the “Property name ” column ofTable 71 , returntrue . - Return
false .
- If the
ClassUnion is present, returnMayContainStrings of theClassUnion . - Return
false .
- If
MayContainStrings of theClassSetOperand istrue , returntrue . - If
ClassUnion is present, returnMayContainStrings of theClassUnion . - Return
false .
- If
MayContainStrings of the firstClassSetOperand isfalse , returnfalse . - If
MayContainStrings of the secondClassSetOperand isfalse , returnfalse . - Return
true .
- If
MayContainStrings of theClassIntersection isfalse , returnfalse . - If
MayContainStrings of theClassSetOperand isfalse , returnfalse . - Return
true .
- Return
MayContainStrings of the firstClassSetOperand .
- Return
MayContainStrings of theClassSubtraction .
- If
MayContainStrings of theClassString istrue , returntrue . - Return
MayContainStrings of theClassStringDisjunctionContents .
- Return
true .
- Return
MayContainStrings of theNonEmptyClassString .
- If
NonEmptyClassString is present, returntrue . - Return
false .
22.2.1.9 Static Semantics: GroupSpecifiersThatMatch ( thisGroupName )
The abstract operation GroupSpecifiersThatMatch takes argument thisGroupName (a
- Let name be the
CapturingGroupName of thisGroupName. - Let pattern be the
Pattern containing thisGroupName. - Let result be a new empty
List . - For each
GroupSpecifier gs that pattern contains, do- If the
CapturingGroupName of gs is name, then- Append gs to result.
- If the
- Return result.
22.2.1.10 Static Semantics: CapturingGroupName
The
- Let idTextUnescaped be the
RegExpIdentifierCodePoints ofRegExpIdentifierName . - Return
CodePointsToString (idTextUnescaped).
22.2.1.11 Static Semantics: RegExpIdentifierCodePoints
The
- Let cp be the
RegExpIdentifierCodePoint ofRegExpIdentifierStart . - Return « cp ».
- Let cps be the
RegExpIdentifierCodePoints of the derivedRegExpIdentifierName . - Let cp be the
RegExpIdentifierCodePoint ofRegExpIdentifierPart . - Return the
list-concatenation of cps and « cp ».
22.2.1.12 Static Semantics: RegExpIdentifierCodePoint
The
- Return the code point matched by
IdentifierStartChar .
- Return the code point matched by
IdentifierPartChar .
- Return the code point whose numeric value is the
CharacterValue ofRegExpUnicodeEscapeSequence .
- Let lead be the code unit whose numeric value is the numeric value of the
code point matched by
UnicodeLeadSurrogate . - Let trail be the code unit whose numeric value is the numeric value of
the code point matched by
UnicodeTrailSurrogate . - Return
UTF16SurrogatePairToCodePoint (lead, trail).
22.2.2 Pattern Semantics
A regular expression pattern is converted into an
A u nor a v. Otherwise, it is a
Unicode pattern. A BMP pattern matches against a String interpreted as consisting of a sequence
of 16-bit values that are Unicode code points in the range of the Basic Multilingual Plane. A
Unicode pattern matches against a String interpreted as consisting of Unicode code points
encoded using UTF-16. In the context of describing the behaviour of a BMP pattern “character”
means a single 16-bit Unicode BMP code point. In the context of describing the behaviour of a
Unicode pattern “character” means a UTF-16 encoded code point (
The syntax and semantics of
For example, consider a pattern expressed in source text as the single non-BMP character
U+1D11E (MUSICAL SYMBOL G CLEF). Interpreted as a Unicode pattern, it would be a single
element (character)
Patterns are passed to the RegExp
An implementation may not actually perform such translations to or from UTF-16, but the semantics of this specification requires that the result of pattern matching be as if such translations were performed.
22.2.2.1 Notation
The descriptions below use the following internal data structures:
-
A CharSetElement is one of the two following entities:
-
If rer.[[UnicodeSets]] is
false , then a CharSetElement is a character in the sense of the Pattern Semantics above. -
If rer.[[UnicodeSets]] is
true , then a CharSetElement is a sequence whose elements are characters in the sense of the Pattern Semantics above. This includes the empty sequence, sequences of one character, and sequences of more than one character. For convenience, when working with CharSetElements of this kind, an individual character is treated interchangeably with a sequence of one character.
-
If rer.[[UnicodeSets]] is
- A CharSet is a mathematical set of CharSetElements.
-
A CaptureRange is a
Record { [[StartIndex]], [[EndIndex]] } that represents the range of characters included in a capture, where [[StartIndex]] is aninteger representing the start index (inclusive) of the range within Input, and [[EndIndex]] is aninteger representing the end index (exclusive) of the range within Input. For anyCaptureRange , these indices must satisfy the invariant that [[StartIndex]] ≤ [[EndIndex]]. -
A MatchState is a
Record { [[Input]], [[EndIndex]], [[Captures]] } where [[Input]] is aList of characters representing the String being matched, [[EndIndex]] is aninteger , and [[Captures]] is aList of values, one for eachleft-capturing parenthesis in the pattern.MatchStates are used to represent partial match states in the regular expression matching algorithms. The [[EndIndex]] is one plus the index of the last input character matched so far by the pattern, while [[Captures]] holds the results of capturing parentheses. The nth element of [[Captures]] is either aCaptureRange representing the range of characters captured by the nth set of capturing parentheses, orundefined if the nth set of capturing parentheses hasn't been reached yet. Due to backtracking, manyMatchStates may be in use at any time during the matching process. -
A MatcherContinuation is an
Abstract Closure that takes oneMatchState argument and returns either aMatchState orfailure . TheMatcherContinuation attempts to match the remaining portion (specified by the closure's captured values) of the pattern against Input, starting at the intermediate state given by itsMatchState argument. If the match succeeds, theMatcherContinuation returns the finalMatchState that it reached; if the match fails, theMatcherContinuation returnsfailure . -
A Matcher is an
Abstract Closure that takes two arguments—aMatchState and aMatcherContinuation —and returns either aMatchState orfailure . AMatcher attempts to match a middle subpattern (specified by the closure's captured values) of the pattern against theMatchState 's [[Input]], starting at the intermediate state given by itsMatchState argument. TheMatcherContinuation argument should be a closure that matches the rest of the pattern. After matching the subpattern of a pattern to obtain a newMatchState , theMatcher then callsMatcherContinuation on that newMatchState to test if the rest of the pattern can match as well. If it can, theMatcher returns theMatchState returned byMatcherContinuation ; if not, theMatcher may try different choices at its choice points, repeatedly callingMatcherContinuation until it either succeeds or all possibilities have been exhausted.
22.2.2.1.1 RegExp Records
A RegExp Record is a
It has the following fields:
| Field Name | Value | Meaning |
|---|---|---|
| [[IgnoreCase]] | a Boolean | indicates whether |
| [[Multiline]] | a Boolean | indicates whether |
| [[DotAll]] | a Boolean | indicates whether |
| [[Unicode]] | a Boolean | indicates whether |
| [[UnicodeSets]] | a Boolean | indicates whether |
| [[CapturingGroupsCount]] | a non-negative |
the number of |
22.2.2.2 Runtime Semantics: CompilePattern
The
- Let m be
CompileSubpattern ofDisjunction with arguments rer andforward . - Return a new
Abstract Closure with parameters (Input, index) that captures rer and m and performs the following steps when called:Assert : Input is aList of characters.Assert : 0 ≤ index ≤ the number of elements in Input.- Let c be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert : y is aMatchState .- Return y.
- Let cap be a
List of rer.[[CapturingGroupsCount]]undefined values, indexed 1 through rer.[[CapturingGroupsCount]]. - Let x be the
MatchState { [[Input]]: Input, [[EndIndex]]: index, [[Captures]]: cap }. - Return m(x, c).
A Pattern compiles to an
22.2.2.3 Runtime Semantics: CompileSubpattern
The
This section is amended in
It is defined piecewise over the following productions:
- Let m1 be
CompileSubpattern ofAlternative with arguments rer and direction. - Let m2 be
CompileSubpattern ofDisjunction with arguments rer and direction. - Return
MatchTwoAlternatives (m1, m2).
The | regular expression operator separates two alternatives. The
pattern first tries to match the left |
produce
/a|ab/.exec("abc")returns the result
/((a)|(ab))((c)|(bc))/.exec("abc")returns the array
["abc", "a", "a", undefined, "bc", undefined, "bc"]and not
["abc", "ab", undefined, "ab", "c", "c", undefined]The order in which the two alternatives are tried is independent of the value of direction.
- Return
EmptyMatcher ().
- Let m1 be
CompileSubpattern ofAlternative with arguments rer and direction. - Let m2 be
CompileSubpattern ofTerm with arguments rer and direction. - Return
MatchSequence (m1, m2, direction).
Consecutive
- Return
CompileAssertion ofAssertion with argument rer.
The resulting
- Return
CompileAtom ofAtom with arguments rer and direction.
- Let m be
CompileAtom ofAtom with arguments rer and direction. - Let q be
CompileQuantifier ofQuantifier . Assert : q.[[Min]] ≤ q.[[Max]].- Let parenIndex be
CountLeftCapturingParensBefore (Term ). - Let parenCount be
CountLeftCapturingParensWithin (Atom ). - Return a new
Matcher with parameters (x, c) that captures m, q, parenIndex, and parenCount and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Return
RepeatMatcher (m, q.[[Min]], q.[[Max]], q.[[Greedy]], x, c, parenIndex, parenCount).
22.2.2.3.1 RepeatMatcher ( m, min, max, greedy, x, c, parenIndex, parenCount )
The abstract operation RepeatMatcher takes arguments m (a
- If max = 0, return c(x).
- Let d be a new
MatcherContinuation with parameters (y) that captures m, min, max, greedy, x, c, parenIndex, and parenCount and performs the following steps when called:Assert : y is aMatchState .- If min = 0 and y.[[EndIndex]] = x.[[EndIndex]], return
failure . - If min = 0, let min2 be 0; otherwise let min2 be min - 1.
- If max = +∞, let max2 be +∞; otherwise let max2 be max - 1.
- Return
RepeatMatcher (m, min2, max2, greedy, y, c, parenIndex, parenCount).
- Let cap be a copy of x.[[Captures]].
- For each
integer k in theinclusive interval from parenIndex + 1 to parenIndex + parenCount, set cap[k] toundefined . - Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- Let xr be the
MatchState { [[Input]]: Input, [[EndIndex]]: e, [[Captures]]: cap }. - If min ≠ 0, return m(xr, d).
- If greedy is
false , then- Let z be c(x).
- If z is not
failure , return z. - Return m(xr, d).
- Let z be m(xr, d).
- If z is not
failure , return z. - Return c(x).
An
If the
Compare
/a[a-z]{2,4}/.exec("abcdefghi")which returns
/a[a-z]{2,4}?/.exec("abcdefghi")which returns
Consider also
/(aa|aabaac|ba|b|c)*/.exec("aabaac")which, by the choice point ordering above, returns the array
["aaba", "ba"]and not any of:
["aabaac", "aabaac"]
["aabaac", "c"]The above ordering of choice points can be used to write a regular expression that calculates the greatest common divisor of two numbers (represented in unary notation). The following example calculates the gcd of 10 and 15:
"aaaaaaaaaa,aaaaaaaaaaaaaaa".replace(/^(a+)\1*,\1+$/, "$1")which returns the gcd in unary notation
Step
/(z)((a+)?(b+)?(c))*/.exec("zaacbbbcac")which returns the array
["zaacbbbcac", "z", "ac", "a", undefined, "c"]and not
["zaacbbbcac", "z", "ac", "a", "bbb", "c"]because each iteration of the outermost * clears all captured
Strings contained in the quantified
Step
/(a*)*/.exec("b")or the slightly more complicated:
/(a*)b\1+/.exec("baaaac")which returns the array
["b", ""]22.2.2.3.2 EmptyMatcher ( )
The abstract operation EmptyMatcher takes no arguments and returns a
- Return a new
Matcher with parameters (x, c) that captures nothing and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Return c(x).
22.2.2.3.3 MatchTwoAlternatives ( m1, m2 )
The abstract operation MatchTwoAlternatives takes arguments m1 (a
- Return a new
Matcher with parameters (x, c) that captures m1 and m2 and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let r be m1(x, c).
- If r is not
failure , return r. - Return m2(x, c).
22.2.2.3.4 MatchSequence ( m1, m2, direction )
The abstract operation MatchSequence takes arguments m1 (a
- If direction is
forward , then- Return a new
Matcher with parameters (x, c) that captures m1 and m2 and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures c and m2 and performs the following steps when called:Assert : y is aMatchState .- Return m2(y, c).
- Return m1(x, d).
- Return a new
- Else,
Assert : direction isbackward .- Return a new
Matcher with parameters (x, c) that captures m1 and m2 and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures c and m1 and performs the following steps when called:Assert : y is aMatchState .- Return m1(y, c).
- Return m2(x, d).
22.2.2.4 Runtime Semantics: CompileAssertion
The
This section is amended in
It is defined piecewise over the following productions:
- Return a new
Matcher with parameters (x, c) that captures rer and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- If e = 0, or if rer.[[Multiline]] is
true and the character Input[e - 1] is matched byLineTerminator , then- Return c(x).
- Return
failure .
Even when the y flag is used with a pattern, ^ always
matches only at the beginning of Input, or (if rer.[[Multiline]] is
- Return a new
Matcher with parameters (x, c) that captures rer and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- Let InputLength be the number of elements in Input.
- If e = InputLength, or if rer.[[Multiline]] is
true and the character Input[e] is matched byLineTerminator , then- Return c(x).
- Return
failure .
- Return a new
Matcher with parameters (x, c) that captures rer and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- Let a be
IsWordChar (rer, Input, e - 1). - Let b be
IsWordChar (rer, Input, e). - If a is
true and b isfalse , or if a isfalse and b istrue , return c(x). - Return
failure .
- Return a new
Matcher with parameters (x, c) that captures rer and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- Let a be
IsWordChar (rer, Input, e - 1). - Let b be
IsWordChar (rer, Input, e). - If a is
true and b istrue , or if a isfalse and b isfalse , return c(x). - Return
failure .
- Let m be
CompileSubpattern ofDisjunction with arguments rer andforward . - Return a new
Matcher with parameters (x, c) that captures m and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert : y is aMatchState .- Return y.
- Let r be m(x, d).
- If r is
failure , returnfailure . Assert : r is aMatchState .- Let cap be r.[[Captures]].
- Let Input be x.[[Input]].
- Let xe be x.[[EndIndex]].
- Let z be the
MatchState { [[Input]]: Input, [[EndIndex]]: xe, [[Captures]]: cap }. - Return c(z).
The form (?= ) specifies a
zero-width positive lookahead. In order for it to succeed, the pattern inside
(?= form (this
unusual behaviour is inherited from Perl). This only matters when the
For example,
/(?=(a+))/.exec("baaabac")matches the empty String immediately after the first b and therefore
returns the array:
["", "aaa"]To illustrate the lack of backtracking into the lookahead, consider:
/(?=(a+))a*b\1/.exec("baaabac")This expression returns
["aba", "a"]and not:
["aaaba", "a"]- Let m be
CompileSubpattern ofDisjunction with arguments rer andforward . - Return a new
Matcher with parameters (x, c) that captures m and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert : y is aMatchState .- Return y.
- Let r be m(x, d).
- If r is not
failure , returnfailure . - Return c(x).
The form (?! ) specifies a
zero-width negative lookahead. In order for it to succeed, the pattern inside
/(.*?)a(?!(a+)b\2c)\2(.*)/.exec("baaabaac")looks for an a not immediately followed by some positive number n of
a's, a b, another n a's (specified by the
first \2) and a c. The second \2 is outside
the negative lookahead, so it matches against
["baaabaac", "ba", undefined, "abaac"]- Let m be
CompileSubpattern ofDisjunction with arguments rer andbackward . - Return a new
Matcher with parameters (x, c) that captures m and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert : y is aMatchState .- Return y.
- Let r be m(x, d).
- If r is
failure , returnfailure . Assert : r is aMatchState .- Let cap be r.[[Captures]].
- Let Input be x.[[Input]].
- Let xe be x.[[EndIndex]].
- Let z be the
MatchState { [[Input]]: Input, [[EndIndex]]: xe, [[Captures]]: cap }. - Return c(z).
- Let m be
CompileSubpattern ofDisjunction with arguments rer andbackward . - Return a new
Matcher with parameters (x, c) that captures m and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert : y is aMatchState .- Return y.
- Let r be m(x, d).
- If r is not
failure , returnfailure . - Return c(x).
22.2.2.4.1 IsWordChar ( rer, Input, e )
The abstract operation IsWordChar takes arguments rer (a
- Let InputLength be the number of elements in Input.
- If e = -1 or e = InputLength, return
false . - Let c be the character Input[e].
- If
WordCharacters (rer) contains c, returntrue . - Return
false .
22.2.2.5 Runtime Semantics: CompileQuantifier
The
- Let qp be
CompileQuantifierPrefix ofQuantifierPrefix . - Return the
Record { [[Min]]: qp.[[Min]], [[Max]]: qp.[[Max]], [[Greedy]]:true }.
- Let qp be
CompileQuantifierPrefix ofQuantifierPrefix . - Return the
Record { [[Min]]: qp.[[Min]], [[Max]]: qp.[[Max]], [[Greedy]]:false }.
22.2.2.6 Runtime Semantics: CompileQuantifierPrefix
The
- Return the
Record { [[Min]]: 0, [[Max]]: +∞ }.
- Return the
Record { [[Min]]: 1, [[Max]]: +∞ }.
- Return the
Record { [[Min]]: 0, [[Max]]: 1 }.
- Let i be the MV of
DecimalDigits (see12.9.3 ). - Return the
Record { [[Min]]: i, [[Max]]: i }.
- Let i be the MV of
DecimalDigits . - Return the
Record { [[Min]]: i, [[Max]]: +∞ }.
- Let i be the MV of the first
DecimalDigits . - Let j be the MV of the second
DecimalDigits . - Return the
Record { [[Min]]: i, [[Max]]: j }.
22.2.2.7 Runtime Semantics: CompileAtom
The
This section is amended in
It is defined piecewise over the following productions:
- Let ch be the character matched by
PatternCharacter . - Let A be a one-element
CharSet containing the character ch. - Return
CharacterSetMatcher (rer, A,false , direction).
- Let A be
AllCharacters (rer). - If rer.[[DotAll]] is not
true , then- Remove from A all characters corresponding to a code point on the
right-hand side of the
LineTerminator production.
- Remove from A all characters corresponding to a code point on the
right-hand side of the
- Return
CharacterSetMatcher (rer, A,false , direction).
- Let cc be
CompileCharacterClass ofCharacterClass with argument rer. - Let cs be cc.[[CharSet]].
- If rer.[[UnicodeSets]] is
false , or if everyCharSetElement of cs consists of a single character (including if cs is empty), returnCharacterSetMatcher (rer, cs, cc.[[Invert]], direction). Assert : cc.[[Invert]] isfalse .- Let lm be an empty
List ofMatchers . - For each
CharSetElement s in cs containing more than 1 character, iterating in descending order of length, do- Let cs2 be a one-element
CharSet containing the last code point of s. - Let m2 be
CharacterSetMatcher (rer, cs2,false , direction). - For each code point c1 in s, iterating backwards from
its second-to-last code point, do
- Let cs1 be a one-element
CharSet containing c1. - Let m1 be
CharacterSetMatcher (rer, cs1,false , direction). - Set m2 to
MatchSequence (m1, m2, direction).
- Let cs1 be a one-element
- Append m2 to lm.
- Let cs2 be a one-element
- Let singles be the
CharSet containing everyCharSetElement of cs that consists of a single character. - Append
CharacterSetMatcher (rer, singles,false , direction) to lm. - If cs contains the empty sequence of characters, append
EmptyMatcher () to lm. - Let m2 be the last
Matcher in lm. - For each
Matcher m1 of lm, iterating backwards from its second-to-last element, do- Set m2 to
MatchTwoAlternatives (m1, m2).
- Set m2 to
- Return m2.
- Let m be
CompileSubpattern ofDisjunction with arguments rer and direction. - Let parenIndex be
CountLeftCapturingParensBefore (Atom ). - Return a new
Matcher with parameters (x, c) that captures direction, m, and parenIndex and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures x, c, direction, and parenIndex and performs the following steps when called:Assert : y is aMatchState .- Let cap be a copy of y.[[Captures]].
- Let Input be x.[[Input]].
- Let xe be x.[[EndIndex]].
- Let ye be y.[[EndIndex]].
- If direction is
forward , thenAssert : xe ≤ ye.- Let r be the
CaptureRange { [[StartIndex]]: xe, [[EndIndex]]: ye }.
- Else,
Assert : direction isbackward .Assert : ye ≤ xe.- Let r be the
CaptureRange { [[StartIndex]]: ye, [[EndIndex]]: xe }.
- Set cap[parenIndex + 1] to r.
- Let z be the
MatchState { [[Input]]: Input, [[EndIndex]]: ye, [[Captures]]: cap }. - Return c(z).
- Return m(x, d).
Parentheses of the form ( ) serve both
to group the components of the \ followed by a non-zero decimal number), referenced in a replace
String, or returned as part of an array from the regular expression matching
(?: ) instead.
- Let addModifiers be the
source text matched by RegularExpressionModifiers . - Let removeModifiers be the empty String.
- Let modifiedRer be
UpdateModifiers (rer,CodePointsToString (addModifiers), removeModifiers). - Return
CompileSubpattern ofDisjunction with arguments modifiedRer and direction.
- Let addModifiers be the
source text matched by the firstRegularExpressionModifiers . - Let removeModifiers be the
source text matched by the secondRegularExpressionModifiers . - Let modifiedRer be
UpdateModifiers (rer,CodePointsToString (addModifiers),CodePointsToString (removeModifiers)). - Return
CompileSubpattern ofDisjunction with arguments modifiedRer and direction.
- Let n be the
CapturingGroupNumber ofDecimalEscape . Assert : n ≤ rer.[[CapturingGroupsCount]].- Return
BackreferenceMatcher (rer, « n », direction).
An escape sequence of the form \ followed by a non-zero decimal number
n matches the result of the nth set of capturing
parentheses (
- Let cv be the
CharacterValue ofCharacterEscape . - Let ch be the character whose character value is cv.
- Let A be a one-element
CharSet containing the character ch. - Return
CharacterSetMatcher (rer, A,false , direction).
- Let cs be
CompileToCharSet ofCharacterClassEscape with argument rer. - If rer.[[UnicodeSets]] is
false , or if everyCharSetElement of cs consists of a single character (including if cs is empty), returnCharacterSetMatcher (rer, cs,false , direction). - Let lm be an empty
List ofMatchers . - For each
CharSetElement s in cs containing more than 1 character, iterating in descending order of length, do- Let cs2 be a one-element
CharSet containing the last code point of s. - Let m2 be
CharacterSetMatcher (rer, cs2,false , direction). - For each code point c1 in s, iterating backwards from
its second-to-last code point, do
- Let cs1 be a one-element
CharSet containing c1. - Let m1 be
CharacterSetMatcher (rer, cs1,false , direction). - Set m2 to
MatchSequence (m1, m2, direction).
- Let cs1 be a one-element
- Append m2 to lm.
- Let cs2 be a one-element
- Let singles be the
CharSet containing everyCharSetElement of cs that consists of a single character. - Append
CharacterSetMatcher (rer, singles,false , direction) to lm. - If cs contains the empty sequence of characters, append
EmptyMatcher () to lm. - Let m2 be the last
Matcher in lm. - For each
Matcher m1 of lm, iterating backwards from its second-to-last element, do- Set m2 to
MatchTwoAlternatives (m1, m2).
- Set m2 to
- Return m2.
- Let matchingGroupSpecifiers be
GroupSpecifiersThatMatch (GroupName ). - Let parenIndices be a new empty
List . - For each
GroupSpecifier groupSpecifier of matchingGroupSpecifiers, do- Let parenIndex be
CountLeftCapturingParensBefore (groupSpecifier). - Append parenIndex to parenIndices.
- Let parenIndex be
- Return
BackreferenceMatcher (rer, parenIndices, direction).
22.2.2.7.1 CharacterSetMatcher ( rer, A, invert, direction )
The abstract operation CharacterSetMatcher takes arguments rer (a
- If rer.[[UnicodeSets]] is
true , thenAssert : invert isfalse .Assert : EveryCharSetElement of A consists of a single character.
- Return a new
Matcher with parameters (x, c) that captures rer, A, invert, and direction and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- If direction is
forward , let f be e + 1. - Else, let f be e - 1.
- Let InputLength be the number of elements in Input.
- If f < 0 or f > InputLength,
return
failure . - Let index be
min (e, f). - Let ch be the character Input[index].
- Let cc be
Canonicalize (rer, ch). - If there exists a
CharSetElement in A containing exactly one character a such thatCanonicalize (rer, a) is cc, let found betrue ; otherwise let found befalse . - If invert is
false and found isfalse , returnfailure . - If invert is
true and found istrue , returnfailure . - Let cap be x.[[Captures]].
- Let y be the
MatchState { [[Input]]: Input, [[EndIndex]]: f, [[Captures]]: cap }. - Return c(y).
22.2.2.7.2 BackreferenceMatcher ( rer, ns, direction )
The abstract operation BackreferenceMatcher takes arguments rer (a
- Return a new
Matcher with parameters (x, c) that captures rer, ns, and direction and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let cap be x.[[Captures]].
- Let r be
undefined . - For each
integer n of ns, do- If cap[n] is not
undefined , thenAssert : r isundefined .- Set r to cap[n].
- If cap[n] is not
- If r is
undefined , return c(x). - Let e be x.[[EndIndex]].
- Let rs be r.[[StartIndex]].
- Let re be r.[[EndIndex]].
- Let len be re - rs.
- If direction is
forward , let f be e + len. - Else, let f be e - len.
- Let InputLength be the number of elements in Input.
- If f < 0 or f > InputLength,
return
failure . - Let g be
min (e, f). - If there exists an
integer i in theinterval from 0 (inclusive) to len (exclusive) such thatCanonicalize (rer, Input[rs + i]) is notCanonicalize (rer, Input[g + i]), returnfailure . - Let y be the
MatchState { [[Input]]: Input, [[EndIndex]]: f, [[Captures]]: cap }. - Return c(y).
22.2.2.7.3 Canonicalize ( rer, ch )
The abstract operation Canonicalize takes arguments rer (a
- If
HasEitherUnicodeFlag (rer) istrue and rer.[[IgnoreCase]] istrue , then- If the file
CaseFolding.txtof the Unicode Character Database provides a simple or common case folding mapping for ch, return the result of applying that mapping to ch. - Return ch.
- If the file
- If rer.[[IgnoreCase]] is
false , return ch. Assert : ch is a UTF-16 code unit.- Let cp be the code point whose numeric value is the numeric value of ch.
- Let u be toUppercase(« cp »), according to the Unicode Default Case Conversion algorithm.
- Let uStr be
CodePointsToString (u). - If the length of uStr ≠ 1, return ch.
- Let cu be uStr's single code unit element.
- If the numeric value of ch ≥ 128 and the numeric value of cu < 128, return ch.
- Return cu.
In case-insignificant matches when ß (U+00DF LATIN SMALL LETTER SHARP S) to
ss or SS. It may however map code points outside the
Basic Latin block to code points within it—for example, ſ (U+017F
LATIN SMALL LETTER LONG S) case-folds to s (U+0073 LATIN SMALL
LETTER S) and K (U+212A KELVIN SIGN) case-folds to k
(U+006B LATIN SMALL LETTER K). Strings containing those code points are matched
by regular expressions such as /[a-z]/ui.
In case-insignificant matches when Ω (U+2126 OHM SIGN) is mapped by
toUppercase to itself but by toCasefold to ω (U+03C9 GREEK SMALL
LETTER OMEGA) along with Ω (U+03A9 GREEK CAPITAL LETTER OMEGA), so
/[ω]/ui and
/[\u03A9]/ui but not by /[ω]/i or
/[\u03A9]/i. Also, no code point outside the Basic Latin block is
mapped to a code point within it, so strings such as /[a-z]/i.
22.2.2.7.4 UpdateModifiers ( rer, add, remove )
The abstract operation UpdateModifiers takes arguments rer (a
Assert : add and remove have no elements in common.- Let ignoreCase be rer.[[IgnoreCase]].
- Let multiline be rer.[[Multiline]].
- Let dotAll be rer.[[DotAll]].
- Let unicode be rer.[[Unicode]].
- Let unicodeSets be rer.[[UnicodeSets]].
- Let capturingGroupsCount be rer.[[CapturingGroupsCount]].
- If remove contains
"i" , set ignoreCase tofalse . - Else if add contains
"i" , set ignoreCase totrue . - If remove contains
"m" , set multiline tofalse . - Else if add contains
"m" , set multiline totrue . - If remove contains
"s" , set dotAll tofalse . - Else if add contains
"s" , set dotAll totrue . - Return the
RegExp Record { [[IgnoreCase]]: ignoreCase, [[Multiline]]: multiline, [[DotAll]]: dotAll, [[Unicode]]: unicode, [[UnicodeSets]]: unicodeSets, [[CapturingGroupsCount]]: capturingGroupsCount }.
22.2.2.8 Runtime Semantics: CompileCharacterClass
The
- Let A be
CompileToCharSet ofClassContents with argument rer. - Return the
Record { [[CharSet]]: A, [[Invert]]:false }.
- Let A be
CompileToCharSet ofClassContents with argument rer. - If rer.[[UnicodeSets]] is
true , then- Return the
Record { [[CharSet]]:CharacterComplement (rer, A), [[Invert]]:false }.
- Return the
- Return the
Record { [[CharSet]]: A, [[Invert]]:true }.
22.2.2.9 Runtime Semantics: CompileToCharSet
The
This section is amended in
It is defined piecewise over the following productions:
- Return the empty
CharSet .
- Let A be
CompileToCharSet ofClassAtom with argument rer. - Let B be
CompileToCharSet ofNonemptyClassRangesNoDash with argument rer. - Return the union of
CharSets A and B.
- Let A be
CompileToCharSet of the firstClassAtom with argument rer. - Let B be
CompileToCharSet of the secondClassAtom with argument rer. - Let C be
CompileToCharSet ofClassContents with argument rer. - Let D be
CharacterRange (A, B). - Return the union of D and C.
- Let A be
CompileToCharSet ofClassAtomNoDash with argument rer. - Let B be
CompileToCharSet ofNonemptyClassRangesNoDash with argument rer. - Return the union of
CharSets A and B.
- Let A be
CompileToCharSet ofClassAtomNoDash with argument rer. - Let B be
CompileToCharSet ofClassAtom with argument rer. - Let C be
CompileToCharSet ofClassContents with argument rer. - Let D be
CharacterRange (A, B). - Return the union of D and C.
Even if the pattern ignores case, the case of the two ends of a range is significant
in determining which characters belong to the range. Thus, for example, the pattern
/[E-F]/i matches only the letters E, F,
e, and f, while the pattern /[E-f]/i matches
all uppercase and lowercase letters in the Unicode Basic Latin block as well as the
symbols [, \, ], ^,
_, and `.
A - character can be treated literally or it can denote a range. It is
treated literally if it is the first or last character of
- Return the
CharSet containing the single character-U+002D (HYPHEN-MINUS).
- Return the
CharSet containing the character matched bySourceCharacter .
- Let cv be the
CharacterValue of thisClassEscape . - Let c be the character whose character value is cv.
- Return the
CharSet containing the single character c.
A \b, \B, and backreferences. Inside a \b means the backspace character, while \B and
backreferences raise errors. Using a backreference inside a
- Return the ten-element
CharSet containing the characters0,1,2,3,4,5,6,7,8, and9.
- Let S be the
CharSet returned byCharacterClassEscape :: d - Return
CharacterComplement (rer, S).
- Return the
CharSet containing all characters corresponding to a code point on the right-hand side of theWhiteSpace orLineTerminator productions.
- Let S be the
CharSet returned byCharacterClassEscape :: s - Return
CharacterComplement (rer, S).
- Return
MaybeSimpleCaseFolding (rer,WordCharacters (rer)).
- Let S be the
CharSet returned byCharacterClassEscape :: w - Return
CharacterComplement (rer, S).
- Return
CompileToCharSet ofUnicodePropertyValueExpression with argument rer.
- Let S be
CompileToCharSet ofUnicodePropertyValueExpression with argument rer. Assert : S contains only single code points.- Return
CharacterComplement (rer, S).
- Let ps be the
source text matched by UnicodePropertyName . - Let p be
UnicodeMatchProperty (rer, ps). Assert : p is a Unicodeproperty name or property alias listed in the “Property name and aliases” column ofTable 69 .- Let vs be the
source text matched by UnicodePropertyValue . - Let v be
UnicodeMatchPropertyValue (p, vs). - Let A be the
CharSet containing all Unicode code points whose character database definition includes the property p with value v. - Return
MaybeSimpleCaseFolding (rer, A).
- Let s be the
source text matched by LoneUnicodePropertyNameOrValue . - If
UnicodeMatchPropertyValue (General_Category, s) is a Unicode property value or property value alias for the General_Category (gc) property listed inPropertyValueAliases.txt, then- Return the
CharSet containing all Unicode code points whose character database definition includes the property “General_Category” with value s.
- Return the
- Let p be
UnicodeMatchProperty (rer, s). Assert : p is a binary Unicode property or binary property alias listed in the “Property name and aliases” column ofTable 70 , or a binary Unicode property of strings listed in the “Property name ” column ofTable 71 .- Let A be the
CharSet containing all CharSetElements whose character database definition includes the property p with value “True”. - Return
MaybeSimpleCaseFolding (rer, A).
- Let A be
CompileToCharSet ofClassSetRange with argument rer. - If
ClassUnion is present, then- Let B be
CompileToCharSet ofClassUnion with argument rer. - Return the union of
CharSets A and B.
- Let B be
- Return A.
- Let A be
CompileToCharSet ofClassSetOperand with argument rer. - If
ClassUnion is present, then- Let B be
CompileToCharSet ofClassUnion with argument rer. - Return the union of
CharSets A and B.
- Let B be
- Return A.
- Let A be
CompileToCharSet of the firstClassSetOperand with argument rer. - Let B be
CompileToCharSet of the secondClassSetOperand with argument rer. - Return the intersection of
CharSets A and B.
- Let A be
CompileToCharSet of theClassIntersection with argument rer. - Let B be
CompileToCharSet of theClassSetOperand with argument rer. - Return the intersection of
CharSets A and B.
- Let A be
CompileToCharSet of the firstClassSetOperand with argument rer. - Let B be
CompileToCharSet of the secondClassSetOperand with argument rer. - Return the
CharSet containing the CharSetElements of A which are not also CharSetElements of B.
- Let A be
CompileToCharSet of theClassSubtraction with argument rer. - Let B be
CompileToCharSet of theClassSetOperand with argument rer. - Return the
CharSet containing the CharSetElements of A which are not also CharSetElements of B.
- Let A be
CompileToCharSet of the firstClassSetCharacter with argument rer. - Let B be
CompileToCharSet of the secondClassSetCharacter with argument rer. - Return
MaybeSimpleCaseFolding (rer,CharacterRange (A, B)).
The result will often consist of two or more ranges. When UnicodeSets is
- Let A be
CompileToCharSet ofClassSetCharacter with argument rer. - Return
MaybeSimpleCaseFolding (rer, A).
- Let A be
CompileToCharSet ofClassStringDisjunction with argument rer. - Return
MaybeSimpleCaseFolding (rer, A).
- Return
CompileToCharSet ofNestedClass with argument rer.
- Return
CompileToCharSet ofClassContents with argument rer.
- Let A be
CompileToCharSet ofClassContents with argument rer. - Return
CharacterComplement (rer, A).
- Return
CompileToCharSet ofCharacterClassEscape with argument rer.
- Return
CompileToCharSet ofClassStringDisjunctionContents with argument rer.
- Let s be
CompileClassSetString ofClassString with argument rer. - Return the
CharSet containing the one string s.
- Let s be
CompileClassSetString ofClassString with argument rer. - Let A be the
CharSet containing the one string s. - Let B be
CompileToCharSet ofClassStringDisjunctionContents with argument rer. - Return the union of
CharSets A and B.
- Let cv be the
CharacterValue of thisClassSetCharacter . - Let c be the character whose character value is cv.
- Return the
CharSet containing the single character c.
- Return the
CharSet containing the single character U+0008 (BACKSPACE).
22.2.2.9.1 CharacterRange ( A, B )
The abstract operation CharacterRange takes arguments A (a
Assert : A and B each contain exactly one character.- Let a be the one character in
CharSet A. - Let b be the one character in
CharSet B. - Let i be the character value of character a.
- Let j be the character value of character b.
Assert : i ≤ j.- Return the
CharSet containing all characters with a character value in theinclusive interval from i to j.
22.2.2.9.2 HasEitherUnicodeFlag ( rer )
The abstract operation HasEitherUnicodeFlag takes argument rer (a
- If rer.[[Unicode]] is
true or rer.[[UnicodeSets]] istrue , then- Return
true .
- Return
- Return
false .
22.2.2.9.3 WordCharacters ( rer )
The abstract operation WordCharacters takes argument rer (a \b, \B,
\w, and \W It performs the following steps when called:
- Let basicWordChars be the
CharSet containing every character inthe ASCII word characters . - Let extraWordChars be the
CharSet containing all characters c such that c is not in basicWordChars butCanonicalize (rer, c) is in basicWordChars. Assert : extraWordChars is empty unlessHasEitherUnicodeFlag (rer) istrue and rer.[[IgnoreCase]] istrue .- Return the union of basicWordChars and extraWordChars.
22.2.2.9.4 AllCharacters ( rer )
The abstract operation AllCharacters takes argument rer (a
- If rer.[[UnicodeSets]] is
true and rer.[[IgnoreCase]] istrue , then- Return the
CharSet containing all Unicode code points c that do not have a Simple Case Folding mapping (that is,scf (c)=c).
- Return the
- Else if
HasEitherUnicodeFlag (rer) istrue , then- Return the
CharSet containing all code point values.
- Return the
- Else,
- Return the
CharSet containing all code unit values.
- Return the
22.2.2.9.5 MaybeSimpleCaseFolding ( rer, A )
The abstract operation MaybeSimpleCaseFolding takes arguments rer (a CaseFolding.txt
of the Unicode Character Database (each of which maps a single code point to another
single code point) to map each
- If rer.[[UnicodeSets]] is
false or rer.[[IgnoreCase]] isfalse , return A. - Let B be a new empty
CharSet . - For each
CharSetElement s of A, do- Let t be an empty sequence of characters.
- For each single code point cp in s, do
- Append
scf (cp) to t.
- Append
- Add t to B.
- Return B.
22.2.2.9.6 CharacterComplement ( rer, S )
The abstract operation CharacterComplement takes arguments rer (a
- Let A be
AllCharacters (rer). - Return the
CharSet containing the CharSetElements of A which are not also CharSetElements of S.
22.2.2.9.7 UnicodeMatchProperty ( rer, p )
The abstract operation UnicodeMatchProperty takes arguments rer (a
- If rer.[[UnicodeSets]] is
true and p is a Unicodeproperty name listed in the “Property name ” column ofTable 71 , then- Return the
List of Unicode code points p.
- Return the
Assert : p is a Unicodeproperty name or property alias listed in the “Property name and aliases” column ofTable 69 orTable 70 .- Let c be the canonical
property name of p as given in the “Canonicalproperty name ” column of the corresponding row. - Return the
List of Unicode code points c.
Implementations must support the Unicode property names and aliases listed in
For example, Script_Extensions (scx (property alias) are valid, but script_extensions
or Scx aren't.
The listed properties form a superset of what UTS18 RL1.2 requires.
The spellings of entries in these tables (including casing) match the spellings
used in the file PropertyAliases.txt
in the Unicode Character Database. The precise spellings in that file are guaranteed
to be stable.
| Canonical |
|
|---|---|
General_Category |
General_Category
|
gc |
|
Script |
Script
|
sc |
|
Script_Extensions |
Script_Extensions
|
scx |
| Canonical |
|
|---|---|
ASCII |
ASCII
|
ASCII_Hex_Digit |
ASCII_Hex_Digit
|
AHex |
|
Alphabetic |
Alphabetic
|
Alpha |
|
Any |
Any
|
Assigned |
Assigned
|
Bidi_Control |
Bidi_Control
|
Bidi_C |
|
Bidi_Mirrored |
Bidi_Mirrored
|
Bidi_M |
|
Case_Ignorable |
Case_Ignorable
|
CI |
|
Cased |
Cased
|
Changes_When_Casefolded |
Changes_When_Casefolded
|
CWCF |
|
Changes_When_Casemapped |
Changes_When_Casemapped
|
CWCM |
|
Changes_When_Lowercased |
Changes_When_Lowercased
|
CWL |
|
Changes_When_NFKC_Casefolded |
Changes_When_NFKC_Casefolded
|
CWKCF |
|
Changes_When_Titlecased |
Changes_When_Titlecased
|
CWT |
|
Changes_When_Uppercased |
Changes_When_Uppercased
|
CWU |
|
Dash |
Dash
|
Default_Ignorable_Code_Point |
Default_Ignorable_Code_Point
|
DI |
|
Deprecated |
Deprecated
|
Dep |
|
Diacritic |
Diacritic
|
Dia |
|
Emoji |
Emoji
|
Emoji_Component |
Emoji_Component
|
EComp |
|
Emoji_Modifier |
Emoji_Modifier
|
EMod |
|
Emoji_Modifier_Base |
Emoji_Modifier_Base
|
EBase |
|
Emoji_Presentation |
Emoji_Presentation
|
EPres |
|
Extended_Pictographic |
Extended_Pictographic
|
ExtPict |
|
Extender |
Extender
|
Ext |
|
Grapheme_Base |
Grapheme_Base
|
Gr_Base |
|
Grapheme_Extend |
Grapheme_Extend
|
Gr_Ext |
|
Hex_Digit |
Hex_Digit
|
Hex |
|
IDS_Binary_Operator |
IDS_Binary_Operator
|
IDSB |
|
IDS_Trinary_Operator |
IDS_Trinary_Operator
|
IDST |
|
ID_Continue |
ID_Continue
|
IDC |
|
ID_Start |
ID_Start
|
IDS |
|
Ideographic |
Ideographic
|
Ideo |
|
Join_Control |
Join_Control
|
Join_C |
|
Logical_Order_Exception |
Logical_Order_Exception
|
LOE |
|
Lowercase |
Lowercase
|
Lower |
|
Math |
Math
|
Noncharacter_Code_Point |
Noncharacter_Code_Point
|
NChar |
|
Pattern_Syntax |
Pattern_Syntax
|
Pat_Syn |
|
Pattern_White_Space |
Pattern_White_Space
|
Pat_WS |
|
Quotation_Mark |
Quotation_Mark
|
QMark |
|
Radical |
Radical
|
Regional_Indicator |
Regional_Indicator
|
RI |
|
Sentence_Terminal |
Sentence_Terminal
|
STerm |
|
Soft_Dotted |
Soft_Dotted
|
SD |
|
Terminal_Punctuation |
Terminal_Punctuation
|
Term |
|
Unified_Ideograph |
Unified_Ideograph
|
UIdeo |
|
Uppercase |
Uppercase
|
Upper |
|
Variation_Selector |
Variation_Selector
|
VS |
|
White_Space |
White_Space
|
space |
|
XID_Continue |
XID_Continue
|
XIDC |
|
XID_Start |
XID_Start
|
XIDS |
Basic_Emoji |
Emoji_Keycap_Sequence |
RGI_Emoji_Modifier_Sequence |
RGI_Emoji_Flag_Sequence |
RGI_Emoji_Tag_Sequence |
RGI_Emoji_ZWJ_Sequence |
RGI_Emoji |
22.2.2.9.8 UnicodeMatchPropertyValue ( p, v )
The abstract operation UnicodeMatchPropertyValue takes arguments p (
Assert : p is a canonical, unaliased Unicodeproperty name listed in the “Canonicalproperty name ” column ofTable 69 .Assert : v is a property value or property value alias for the Unicode property p listed inPropertyValueAliases.txt.- Let value be the canonical property value of v as given in the “Canonical property value” column of the corresponding row.
- Return the
List of Unicode code points value.
Implementations must support the Unicode property values and property value aliases
listed in PropertyValueAliases.txt
for the properties listed in
For example, Xpeo and Old_Persian are valid
Script_Extensions values, but xpeo and
Old Persian aren't.
This algorithm differs from the matching
rules for symbolic values listed in UAX44: case, Is prefix is not supported.
22.2.2.10 Runtime Semantics: CompileClassSetString
The
- Return an empty sequence of characters.
- Return
CompileClassSetString ofNonEmptyClassString with argument rer.
- Let cs be
CompileToCharSet ofClassSetCharacter with argument rer. - Let s1 be the sequence of characters that is the single
CharSetElement of cs. - If
NonEmptyClassString is present, then- Let s2 be
CompileClassSetString ofNonEmptyClassString with argument rer. - Return the concatenation of s1 and s2.
- Let s2 be
- Return s1.
22.2.3 Abstract Operations for RegExp Creation
22.2.3.1 RegExpCreate ( P, F )
The abstract operation RegExpCreate takes arguments P (an
- Let obj be !
RegExpAlloc (%RegExp% ). - Return ?
RegExpInitialize (obj, P, F).
22.2.3.2 RegExpAlloc ( newTarget )
The abstract operation RegExpAlloc takes argument newTarget (a
- Let obj be ?
OrdinaryCreateFromConstructor (newTarget,"%RegExp.prototype%" , « [[OriginalSource]], [[OriginalFlags]], [[RegExpRecord]], [[RegExpMatcher]] »). - Perform !
DefinePropertyOrThrow (obj,"lastIndex" , PropertyDescriptor { [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return obj.
22.2.3.3 RegExpInitialize ( obj, pattern, flags )
The abstract operation RegExpInitialize takes arguments obj (an Object),
pattern (an
- If pattern is
undefined , let P be the empty String. - Else, let P be ?
ToString (pattern). - If flags is
undefined , let F be the empty String. - Else, let F be ?
ToString (flags). - If F contains any code unit other than
"d" ,"g" ,"i" ,"m" ,"s" ,"u" ,"v" , or"y" , or if F contains any code unit more than once, throw aSyntaxError exception. - If F contains
"i" , let i betrue ; else let i befalse . - If F contains
"m" , let m betrue ; else let m befalse . - If F contains
"s" , let s betrue ; else let s befalse . - If F contains
"u" , let u betrue ; else let u befalse . - If F contains
"v" , let v betrue ; else let v befalse . - If u is
true or v istrue , then- Let patternText be
StringToCodePoints (P).
- Let patternText be
- Else,
- Let patternText be the result of interpreting each of P's 16-bit elements as a Unicode BMP code point. UTF-16 decoding is not applied to the elements.
- Let parseResult be
ParsePattern (patternText, u, v). - If parseResult is a non-empty
List ofSyntaxError objects, throw aSyntaxError exception. Assert : parseResult is aPattern Parse Node .- Set obj.[[OriginalSource]] to P.
- Set obj.[[OriginalFlags]] to F.
- Let capturingGroupsCount be
CountLeftCapturingParensWithin (parseResult). - Let rer be the
RegExp Record { [[IgnoreCase]]: i, [[Multiline]]: m, [[DotAll]]: s, [[Unicode]]: u, [[UnicodeSets]]: v, [[CapturingGroupsCount]]: capturingGroupsCount }. - Set obj.[[RegExpRecord]] to rer.
- Set obj.[[RegExpMatcher]] to
CompilePattern of parseResult with argument rer. - Perform ?
Set (obj,"lastIndex" ,+0 𝔽,true ). - Return obj.
22.2.3.4 Static Semantics: ParsePattern ( patternText, u, v )
The abstract operation ParsePattern takes arguments patternText (a sequence of
Unicode code points), u (a Boolean), and v (a Boolean) and returns a
This section is amended in
It performs the following steps when called:
- If v is
true and u istrue , then- Let parseResult be a
List containing one or moreSyntaxError objects.
- Let parseResult be a
- Else if v is
true , then - Else if u is
true , then - Else,
- Return parseResult.
22.2.4 The RegExp Constructor
The RegExp
- is %RegExp%.
- is the initial value of the
"RegExp" property of theglobal object . - creates and initializes a new RegExp object when called as a
constructor . - when called as a function rather than as a
constructor , returns either a new RegExp object, or the argument itself if the only argument is a RegExp object. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified RegExp behaviour must include asupercall to the RegExpconstructor to create and initialize subclass instances with the necessary internal slots.
22.2.4.1 RegExp ( pattern, flags )
This function performs the following steps when called:
- Let patternIsRegExp be ?
IsRegExp (pattern). - If NewTarget is
undefined , then- Let newTarget be the
active function object . - If patternIsRegExp is
true and flags isundefined , then
- Let newTarget be the
- Else,
- Let newTarget be NewTarget.
- If pattern
is an Object and pattern has a [[RegExpMatcher]] internal slot, then- Let P be pattern.[[OriginalSource]].
- If flags is
undefined , let F be pattern.[[OriginalFlags]]. - Else, let F be flags.
- Else if patternIsRegExp is
true , then - Else,
- Let P be pattern.
- Let F be flags.
- Let O be ?
RegExpAlloc (newTarget). - Return ?
RegExpInitialize (O, P, F).
If pattern is supplied using a
22.2.5 Properties of the RegExp Constructor
The RegExp
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
22.2.5.1 RegExp.escape ( S )
This function returns a copy of S in which characters that are potentially special
in a regular expression
It performs the following steps when called:
- If S
is not a String , throw aTypeError exception. - Let escaped be the empty String.
- Let cpList be
StringToCodePoints (S). - For each code point cp of cpList, do
- If escaped is the empty String and cp is matched by
either
DecimalDigit orAsciiLetter , then- NOTE: Escaping a leading digit ensures that output corresponds with
pattern text which may be used after a
\0character escape or aDecimalEscape such as\1and still match S rather than be interpreted as an extension of the preceding escape sequence. Escaping a leading ASCII letter does the same for the context after\c. - Let numericValue be the numeric value of cp.
- Let hex be
Number::toString (𝔽 (numericValue), 16). Assert : The length of hex is 2.- Set escaped to the
string-concatenation of the code unit 0x005C (REVERSE SOLIDUS),"x" , and hex.
- NOTE: Escaping a leading digit ensures that output corresponds with
pattern text which may be used after a
- Else,
- Set escaped to the
string-concatenation of escaped andEncodeForRegExpEscape (cp).
- Set escaped to the
- If escaped is the empty String and cp is matched by
either
- Return escaped.
Despite having similar names, RegExp.escape do not perform similar actions. The former escapes a
pattern for representation as a string, while this function escapes a string for
representation inside a pattern.
22.2.5.1.1 EncodeForRegExpEscape ( cp )
The abstract operation EncodeForRegExpEscape takes argument cp (a code point)
and returns a String. It returns a String representing a
- If cp is matched by
SyntaxCharacter or cp is U+002F (SOLIDUS), then- Return the
string-concatenation of 0x005C (REVERSE SOLIDUS) andUTF16EncodeCodePoint (cp).
- Return the
- Else if cp is a code point listed in the “Code Point” column of
Table 67 , then- Return the
string-concatenation of 0x005C (REVERSE SOLIDUS) and the string in the “ControlEscape” column of the row whose “Code Point” column contains cp.
- Return the
- Let otherPunctuators be the
string-concatenation of",-=<>#&!%:;@~'`" and the code unit 0x0022 (QUOTATION MARK). - Let toEscape be
StringToCodePoints (otherPunctuators). - If toEscape contains cp, cp is matched by
either
WhiteSpace orLineTerminator , or cp has the same numeric value as aleading surrogate ortrailing surrogate , then- Let cpNum be the numeric value of cp.
- If cpNum ≤ 0xFF, then
- Let hex be
Number::toString (𝔽 (cpNum), 16). - Return the
string-concatenation of the code unit 0x005C (REVERSE SOLIDUS),"x" , andStringPad (hex, 2,"0" ,start ).
- Let hex be
- Let escaped be the empty String.
- Let codeUnits be
UTF16EncodeCodePoint (cp). - For each code unit cu of codeUnits, do
- Set escaped to the
string-concatenation of escaped andUnicodeEscape (cu).
- Set escaped to the
- Return escaped.
- Return
UTF16EncodeCodePoint (cp).
22.2.5.2 RegExp.prototype
The initial value of RegExp.prototype is the
This property has the attributes { [[Writable]]:
22.2.5.3 get RegExp [ %Symbol.species% ]
RegExp[%Symbol.species%] is an
- Return the
this value.
The value of the
RegExp prototype methods normally use their
22.2.6 Properties of the RegExp Prototype Object
The RegExp prototype object:
- is %RegExp.prototype%.
- is an
ordinary object . - is not a RegExp instance and does not have a [[RegExpMatcher]] internal slot or any of the other internal slots of RegExp instance objects.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% .
The RegExp prototype object does not have a
22.2.6.1 RegExp.prototype.constructor
The initial value of RegExp.prototype.constructor is
22.2.6.2 RegExp.prototype.exec ( string )
This method searches string for an occurrence of the regular expression pattern
and returns an Array containing the results of the match, or
It performs the following steps when called:
- Let R be the
this value. - Perform ?
RequireInternalSlot (R, [[RegExpMatcher]]). - Let S be ?
ToString (string). - Return ?
RegExpBuiltinExec (R, S).
22.2.6.3 get RegExp.prototype.dotAll
RegExp.prototype.dotAll is an
- Let R be the
this value. - Let cu be the code unit 0x0073 (LATIN SMALL LETTER S).
- Return ?
RegExpHasFlag (R, cu).
22.2.6.4 get RegExp.prototype.flags
RegExp.prototype.flags is an
- Let R be the
this value. - If R
is not an Object , throw aTypeError exception. - Let codeUnits be a new empty
List . - Let hasIndices be
ToBoolean (?Get (R,"hasIndices" )). - If hasIndices is
true , append the code unit 0x0064 (LATIN SMALL LETTER D) to codeUnits. - Let global be
ToBoolean (?Get (R,"global" )). - If global is
true , append the code unit 0x0067 (LATIN SMALL LETTER G) to codeUnits. - Let ignoreCase be
ToBoolean (?Get (R,"ignoreCase" )). - If ignoreCase is
true , append the code unit 0x0069 (LATIN SMALL LETTER I) to codeUnits. - Let multiline be
ToBoolean (?Get (R,"multiline" )). - If multiline is
true , append the code unit 0x006D (LATIN SMALL LETTER M) to codeUnits. - Let dotAll be
ToBoolean (?Get (R,"dotAll" )). - If dotAll is
true , append the code unit 0x0073 (LATIN SMALL LETTER S) to codeUnits. - Let unicode be
ToBoolean (?Get (R,"unicode" )). - If unicode is
true , append the code unit 0x0075 (LATIN SMALL LETTER U) to codeUnits. - Let unicodeSets be
ToBoolean (?Get (R,"unicodeSets" )). - If unicodeSets is
true , append the code unit 0x0076 (LATIN SMALL LETTER V) to codeUnits. - Let sticky be
ToBoolean (?Get (R,"sticky" )). - If sticky is
true , append the code unit 0x0079 (LATIN SMALL LETTER Y) to codeUnits. - Return the String value whose code units are the elements of the
List codeUnits. If codeUnits has no elements, the empty String is returned.
22.2.6.4.1 RegExpHasFlag ( R, codeUnit )
The abstract operation RegExpHasFlag takes arguments R (an
- If R
is not an Object , throw aTypeError exception. - If R does not have an [[OriginalFlags]]
internal slot, then
- If
SameValue (R,%RegExp.prototype% ) istrue , returnundefined . - Otherwise, throw a
TypeError exception.
- If
- Let flags be R.[[OriginalFlags]].
- If flags contains codeUnit, return
true . - Return
false .
22.2.6.5 get RegExp.prototype.global
RegExp.prototype.global is an
- Let R be the
this value. - Let cu be the code unit 0x0067 (LATIN SMALL LETTER G).
- Return ?
RegExpHasFlag (R, cu).
22.2.6.6 get RegExp.prototype.hasIndices
RegExp.prototype.hasIndices is an
- Let R be the
this value. - Let cu be the code unit 0x0064 (LATIN SMALL LETTER D).
- Return ?
RegExpHasFlag (R, cu).
22.2.6.7 get RegExp.prototype.ignoreCase
RegExp.prototype.ignoreCase is an
- Let R be the
this value. - Let cu be the code unit 0x0069 (LATIN SMALL LETTER I).
- Return ?
RegExpHasFlag (R, cu).
22.2.6.8 RegExp.prototype [ %Symbol.match% ] ( string )
This method performs the following steps when called:
- Let rx be the
this value. - If rx
is not an Object , throw aTypeError exception. - Let S be ?
ToString (string). - Let flags be ?
ToString (?Get (rx,"flags" )). - If flags does not contain
"g" , then- Return ?
RegExpExec (rx, S).
- Return ?
- Else,
- If flags contains
"u" or flags contains"v" , let fullUnicode betrue ; otherwise let fullUnicode befalse . - Perform ?
Set (rx,"lastIndex" ,+0 𝔽,true ). - Let A be !
ArrayCreate (0). - Let n be 0.
- Repeat,
- Let result be ?
RegExpExec (rx, S). - If result is
null , then- If n = 0, return
null . - Return A.
- If n = 0, return
- Else,
- Let matchStr be ?
ToString (?Get (result,"0" )). - Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), matchStr). - If matchStr is the empty String, then
- Set n to n + 1.
- Let matchStr be ?
- Let result be ?
- If flags contains
The value of the
The
22.2.6.9 RegExp.prototype [ %Symbol.matchAll% ] ( string )
This method performs the following steps when called:
- Let R be the
this value. - If R
is not an Object , throw aTypeError exception. - Let S be ?
ToString (string). - Let C be ?
SpeciesConstructor (R,%RegExp% ). - Let flags be ?
ToString (?Get (R,"flags" )). - Let matcher be ?
Construct (C, « R, flags »). - Let lastIndex be ?
ToLength (?Get (R,"lastIndex" )). - Perform ?
Set (matcher,"lastIndex" , lastIndex,true ). - If flags contains
"g" , let global betrue . - Else, let global be
false . - If flags contains
"u" or flags contains"v" , let fullUnicode betrue . - Else, let fullUnicode be
false . - Return
CreateRegExpStringIterator (matcher, S, global, fullUnicode).
The value of the
22.2.6.10 get RegExp.prototype.multiline
RegExp.prototype.multiline is an
- Let R be the
this value. - Let cu be the code unit 0x006D (LATIN SMALL LETTER M).
- Return ?
RegExpHasFlag (R, cu).
22.2.6.11 RegExp.prototype [ %Symbol.replace% ] ( string, replaceValue )
This method performs the following steps when called:
- Let rx be the
this value. - If rx
is not an Object , throw aTypeError exception. - Let S be ?
ToString (string). - Let lengthS be the length of S.
- Let functionalReplace be
IsCallable (replaceValue). - If functionalReplace is
false , then- Set replaceValue to ?
ToString (replaceValue).
- Set replaceValue to ?
- Let flags be ?
ToString (?Get (rx,"flags" )). - If flags contains
"g" , let global betrue ; otherwise let global befalse . - If global is
true , then- Perform ?
Set (rx,"lastIndex" ,+0 𝔽,true ).
- Perform ?
- Let results be a new empty
List . - Let done be
false . - Repeat, while done is
false ,- Let result be ?
RegExpExec (rx, S). - If result is
null , then- Set done to
true .
- Set done to
- Else,
- Let result be ?
- Let accumulatedResult be the empty String.
- Let nextSourcePosition be 0.
- For each element result of results, do
- Let resultLength be ?
LengthOfArrayLike (result). - Let nCaptures be
max (resultLength - 1, 0). - Let matched be ?
ToString (?Get (result,"0" )). - Let matchLength be the length of matched.
- Let position be ?
ToIntegerOrInfinity (?Get (result,"index" )). - Set position to the result of
clamping position between 0 and lengthS. - Let captures be a new empty
List . - Let n be 1.
- Repeat, while n ≤ nCaptures,
- Let capN be ?
Get (result, !ToString (𝔽 (n))). - If capN is not
undefined , then- Set capN to ?
ToString (capN).
- Set capN to ?
- Append capN to captures.
- NOTE: When n = 1, the preceding step puts the first element into captures (at index 0). More generally, the nth capture (the characters captured by the nth set of capturing parentheses) is at captures[n - 1].
- Set n to n + 1.
- Let capN be ?
- Let namedCaptures be ?
Get (result,"groups" ). - If functionalReplace is
true , then- Let replacerArgs be the
list-concatenation of « matched », captures, and «𝔽 (position), S ». - If namedCaptures is not
undefined , then- Append namedCaptures to replacerArgs.
- Let replacementValue be ?
Call (replaceValue,undefined , replacerArgs). - Let replacementString be ?
ToString (replacementValue).
- Let replacerArgs be the
- Else,
- If namedCaptures is not
undefined , then- Set namedCaptures to ?
ToObject (namedCaptures).
- Set namedCaptures to ?
- Let replacementString be ?
GetSubstitution (matched, S, position, captures, namedCaptures, replaceValue).
- If namedCaptures is not
- If position ≥ nextSourcePosition, then
- NOTE: position should not normally move backwards. If it does, it is an indication of an ill-behaving RegExp subclass or use of an access triggered side-effect to change the global flag or other characteristics of rx. In such cases, the corresponding substitution is ignored.
- Set accumulatedResult to the
string-concatenation of accumulatedResult, thesubstring of S from nextSourcePosition to position, and replacementString. - Set nextSourcePosition to position + matchLength.
- Let resultLength be ?
- If nextSourcePosition ≥ lengthS, return accumulatedResult.
- Return the
string-concatenation of accumulatedResult and thesubstring of S from nextSourcePosition.
The value of the
22.2.6.12 RegExp.prototype [ %Symbol.search% ] ( string )
This method performs the following steps when called:
- Let rx be the
this value. - If rx
is not an Object , throw aTypeError exception. - Let S be ?
ToString (string). - Let previousLastIndex be ?
Get (rx,"lastIndex" ). - If previousLastIndex is not
+0 𝔽, then- Perform ?
Set (rx,"lastIndex" ,+0 𝔽,true ).
- Perform ?
- Let result be ?
RegExpExec (rx, S). - Let currentLastIndex be ?
Get (rx,"lastIndex" ). - If
SameValue (currentLastIndex, previousLastIndex) isfalse , then- Perform ?
Set (rx,"lastIndex" , previousLastIndex,true ).
- Perform ?
- If result is
null , return-1 𝔽. - Return ?
Get (result,"index" ).
The value of the
The
22.2.6.13 get RegExp.prototype.source
RegExp.prototype.source is an
- Let R be the
this value. - If R
is not an Object , throw aTypeError exception. - If R does not have an [[OriginalSource]]
internal slot, then
- If
SameValue (R,%RegExp.prototype% ) istrue , return"(?:)" . - Otherwise, throw a
TypeError exception.
- If
Assert : R has an [[OriginalFlags]] internal slot.- Let src be R.[[OriginalSource]].
- Let flags be R.[[OriginalFlags]].
- Return
EscapeRegExpPattern (src, flags).
22.2.6.13.1 EscapeRegExpPattern ( P, F )
The abstract operation EscapeRegExpPattern takes arguments P (a String) and F (a String) and returns a String. It performs the following steps when called:
- If F contains
"v" , then- Let patternSymbol be
Pattern .[+UnicodeMode, +UnicodeSetsMode]
- Let patternSymbol be
- Else if F contains
"u" , then- Let patternSymbol be
Pattern .[+UnicodeMode, ~UnicodeSetsMode]
- Let patternSymbol be
- Else,
- Let patternSymbol be
Pattern .[~UnicodeMode, ~UnicodeSetsMode]
- Let patternSymbol be
- Let S be a String in the form of a patternSymbol
equivalent to P interpreted as UTF-16 encoded Unicode code points
(
6.1.4 ), in which certain code points are escaped as described below. S may or may not differ from P; however, theAbstract Closure that would result from evaluating S as a patternSymbol must behave identically to theAbstract Closure given by the constructed object's [[RegExpMatcher]] internal slot. Multiple calls to this abstract operation using the same values for P and F must produce identical results. - The code points
/or anyLineTerminator occurring in the pattern shall be escaped in S as necessary to ensure that thestring-concatenation of"/" , S,"/" , and F can be parsed (in an appropriate lexical context) as aRegularExpressionLiteral that behaves identically to the constructed regular expression. For example, if P is"/" , then S could be"\/" or"\u002F" , among other possibilities, but not"/" , because///followed by F would be parsed as aSingleLineComment rather than aRegularExpressionLiteral . If P is the empty String, this specification can be met by letting S be"(?:)" . - Return S.
Despite having similar names, RegExp.escape and EscapeRegExpPattern
do not perform similar actions. The former escapes a string for representation
inside a pattern, while this function escapes a pattern for representation as a
string.
22.2.6.14 RegExp.prototype [ %Symbol.split% ] ( string, limit )
This method returns an Array into which substrings of the result of converting
string to a String have been stored. The substrings are determined by
searching from left to right for matches of the
The /a*?/[Symbol.split]("ab") evaluates to the array
["a", "b"], while /a*/[Symbol.split]("ab") evaluates to
the array ["","b"].)
If string is (or converts to) the empty String, the result depends on whether the regular expression can match the empty String. If it can, the result array contains no elements. Otherwise, the result array contains one element, which is the empty String.
If the regular expression contains capturing parentheses, then each time
separator is matched the results (including any
/<(\/)?([^<>]+)>/[Symbol.split]("A<B>bold</B>and<CODE>coded</CODE>")evaluates to the array
["A", undefined, "B", "bold", "/", "B", "and", undefined, "CODE", "coded", "/", "CODE", ""]If limit is not
This method performs the following steps when called:
- Let rx be the
this value. - If rx
is not an Object , throw aTypeError exception. - Let S be ?
ToString (string). - Let C be ?
SpeciesConstructor (rx,%RegExp% ). - Let flags be ?
ToString (?Get (rx,"flags" )). - If flags contains
"u" or flags contains"v" , let unicodeMatching betrue . - Else, let unicodeMatching be
false . - If flags contains
"y" , let newFlags be flags. - Else, let newFlags be the
string-concatenation of flags and"y" . - Let splitter be ?
Construct (C, « rx, newFlags »). - Let A be !
ArrayCreate (0). - Let lengthA be 0.
- If limit is
undefined , let lim be 232 - 1; else let lim beℝ (?ToUint32 (limit)). - If lim = 0, return A.
- If S is the empty String, then
- Let z be ?
RegExpExec (splitter, S). - If z is not
null , return A. - Perform !
CreateDataPropertyOrThrow (A,"0" , S). - Return A.
- Let z be ?
- Let size be the length of S.
- Let p be 0.
- Let q be p.
- Repeat, while q < size,
- Perform ?
Set (splitter,"lastIndex" ,𝔽 (q),true ). - Let z be ?
RegExpExec (splitter, S). - If z is
null , then- Set q to
AdvanceStringIndex (S, q, unicodeMatching).
- Set q to
- Else,
- Let e be
ℝ (?ToLength (?Get (splitter,"lastIndex" ))). - Set e to
min (e, size). - If e = p, then
- Set q to
AdvanceStringIndex (S, q, unicodeMatching).
- Set q to
- Else,
- Let T be the
substring of S from p to q. - Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (lengthA)), T). - Set lengthA to lengthA + 1.
- If lengthA = lim, return A.
- Set p to e.
- Let numberOfCaptures be ?
LengthOfArrayLike (z). - Set numberOfCaptures to
max (numberOfCaptures - 1, 0). - Let i be 1.
- Repeat, while i ≤ numberOfCaptures,
- Set q to p.
- Let T be the
- Let e be
- Perform ?
- Let T be the
substring of S from p to size. - Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (lengthA)), T). - Return A.
The value of the
This method ignores the value of the
22.2.6.15 get RegExp.prototype.sticky
RegExp.prototype.sticky is an
- Let R be the
this value. - Let cu be the code unit 0x0079 (LATIN SMALL LETTER Y).
- Return ?
RegExpHasFlag (R, cu).
22.2.6.16 RegExp.prototype.test ( S )
This method performs the following steps when called:
- Let R be the
this value. - If R
is not an Object , throw aTypeError exception. - Let string be ?
ToString (S). - Let match be ?
RegExpExec (R, string). - If match is not
null , returntrue ; else returnfalse .
22.2.6.17 RegExp.prototype.toString ( )
- Let R be the
this value. - If R
is not an Object , throw aTypeError exception. - Let pattern be ?
ToString (?Get (R,"source" )). - Let flags be ?
ToString (?Get (R,"flags" )). - Let result be the
string-concatenation of"/" , pattern,"/" , and flags. - Return result.
The returned String has the form of a
22.2.6.18 get RegExp.prototype.unicode
RegExp.prototype.unicode is an
- Let R be the
this value. - Let cu be the code unit 0x0075 (LATIN SMALL LETTER U).
- Return ?
RegExpHasFlag (R, cu).
22.2.6.19 get RegExp.prototype.unicodeSets
RegExp.prototype.unicodeSets is an
- Let R be the
this value. - Let cu be the code unit 0x0076 (LATIN SMALL LETTER V).
- Return ?
RegExpHasFlag (R, cu).
22.2.7 Abstract Operations for RegExp Matching
22.2.7.1 RegExpExec ( R, S )
The abstract operation RegExpExec takes arguments R (an Object) and S
(a String) and returns either a
- Let exec be ?
Get (R,"exec" ). - If
IsCallable (exec) istrue , then- Let result be ?
Call (exec, R, « S »). - If result
is not an Object and result is notnull , throw aTypeError exception. - Return result.
- Let result be ?
- Perform ?
RequireInternalSlot (R, [[RegExpMatcher]]). - Return ?
RegExpBuiltinExec (R, S).
If a callable
22.2.7.2 RegExpBuiltinExec ( R, S )
The abstract operation RegExpBuiltinExec takes arguments R (an initialized RegExp
instance) and S (a String) and returns either a
- Let length be the length of S.
- Let lastIndex be
ℝ (?ToLength (?Get (R,"lastIndex" ))). - Let flags be R.[[OriginalFlags]].
- If flags contains
"g" , let global betrue ; else let global befalse . - If flags contains
"y" , let sticky betrue ; else let sticky befalse . - If flags contains
"d" , let hasIndices betrue ; else let hasIndices befalse . - If global is
false and sticky isfalse , set lastIndex to 0. - Let matcher be R.[[RegExpMatcher]].
- If flags contains
"u" or flags contains"v" , let fullUnicode betrue ; else let fullUnicode befalse . - Let matchSucceeded be
false . - If fullUnicode is
true , let input beStringToCodePoints (S); otherwise let input be aList whose elements are the code units that are the elements of S. - NOTE: Each element of input is considered to be a character.
- Repeat, while matchSucceeded is
false ,- If lastIndex > length, then
- If global is
true or sticky istrue , then- Perform ?
Set (R,"lastIndex" ,+0 𝔽,true ).
- Perform ?
- Return
null .
- If global is
- Let inputIndex be the index into input of the character that was obtained from element lastIndex of S.
- Let r be matcher(input, inputIndex).
- If r is
failure , then- If sticky is
true , then- Perform ?
Set (R,"lastIndex" ,+0 𝔽,true ). - Return
null .
- Perform ?
- Set lastIndex to
AdvanceStringIndex (S, lastIndex, fullUnicode).
- If sticky is
- Else,
Assert : r is aMatchState .- Set matchSucceeded to
true .
- If lastIndex > length, then
- Let e be r.[[EndIndex]].
- If fullUnicode is
true , set e toGetStringIndex (S, e). - If global is
true or sticky istrue , then - Let n be the number of elements in r.[[Captures]].
Assert : n = R.[[RegExpRecord]].[[CapturingGroupsCount]].Assert : n < 232 - 1.- Let A be !
ArrayCreate (n + 1). Assert : Themathematical value of A's"length" property is n + 1.- Perform !
CreateDataPropertyOrThrow (A,"index" ,𝔽 (lastIndex)). - Perform !
CreateDataPropertyOrThrow (A,"input" , S). - Let match be the
Match Record { [[StartIndex]]: lastIndex, [[EndIndex]]: e }. - Let indices be a new empty
List . - Let groupNames be a new empty
List . - Append match to indices.
- Let matchedSubstr be
GetMatchString (S, match). - Perform !
CreateDataPropertyOrThrow (A,"0" , matchedSubstr). - If R contains any
GroupName , then- Let groups be
OrdinaryObjectCreate (null ). - Let hasGroups be
true .
- Let groups be
- Else,
- Let groups be
undefined . - Let hasGroups be
false .
- Let groups be
- Perform !
CreateDataPropertyOrThrow (A,"groups" , groups). - Let matchedGroupNames be a new empty
List . - For each
integer i such that 1 ≤ i ≤ n, in ascending order, do- Let captureI be ith element of r.[[Captures]].
- If captureI is
undefined , then- Let capturedValue be
undefined . - Append
undefined to indices.
- Let capturedValue be
- Else,
- Let captureStart be captureI.[[StartIndex]].
- Let captureEnd be captureI.[[EndIndex]].
- If fullUnicode is
true , then- Set captureStart to
GetStringIndex (S, captureStart). - Set captureEnd to
GetStringIndex (S, captureEnd).
- Set captureStart to
- Let capture be the
Match Record { [[StartIndex]]: captureStart, [[EndIndex]]: captureEnd }. - Let capturedValue be
GetMatchString (S, capture). - Append capture to indices.
- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (i)), capturedValue). - If the ith capture of R was defined with a
GroupName , then- Let s be the
CapturingGroupName of thatGroupName . - If matchedGroupNames contains s, then
Assert : capturedValue isundefined .- Append
undefined to groupNames.
- Else,
- If capturedValue is not
undefined , append s to matchedGroupNames. - NOTE: If there are multiple groups named s,
groups may already have an s property
at this point. However, because groups is an
ordinary object whose properties are all writabledata properties , the call toCreateDataPropertyOrThrow is nevertheless guaranteed to succeed. - Perform !
CreateDataPropertyOrThrow (groups, s, capturedValue). - Append s to groupNames.
- If capturedValue is not
- Let s be the
- Else,
- Append
undefined to groupNames.
- Append
- If hasIndices is
true , then- Let indicesArray be
MakeMatchIndicesIndexPairArray (S, indices, groupNames, hasGroups). - Perform !
CreateDataPropertyOrThrow (A,"indices" , indicesArray).
- Let indicesArray be
- Return A.
22.2.7.3 AdvanceStringIndex ( S, index, unicode )
The abstract operation AdvanceStringIndex takes arguments S (a String),
index (a non-negative
Assert : index ≤ 253 - 1.- If unicode is
false , return index + 1. - Let length be the length of S.
- If index + 1 ≥ length, return index + 1.
- Let cp be
CodePointAt (S, index). - Return index + cp.[[CodeUnitCount]].
22.2.7.4 GetStringIndex ( S, codePointIndex )
The abstract operation GetStringIndex takes arguments S (a String) and
codePointIndex (a non-negative
- If S is the empty String, return 0.
- Let len be the length of S.
- Let codeUnitCount be 0.
- Let codePointCount be 0.
- Repeat, while codeUnitCount < len,
- If codePointCount = codePointIndex, return codeUnitCount.
- Let cp be
CodePointAt (S, codeUnitCount). - Set codeUnitCount to codeUnitCount + cp.[[CodeUnitCount]].
- Set codePointCount to codePointCount + 1.
- Return len.
22.2.7.5 Match Records
A Match Record is a
Match Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[StartIndex]] | a non-negative |
The number of code units from the start of a string at which the match begins (inclusive). |
| [[EndIndex]] | an |
The number of code units from the start of a string at which the match ends (exclusive). |
22.2.7.6 GetMatchString ( S, match )
The abstract operation GetMatchString takes arguments S (a String) and
match (a
22.2.7.7 GetMatchIndexPair ( S, match )
The abstract operation GetMatchIndexPair takes arguments S (a String) and
match (a
Assert : match.[[StartIndex]] ≤ match.[[EndIndex]] ≤ the length of S.- Return
CreateArrayFromList («𝔽 (match.[[StartIndex]]),𝔽 (match.[[EndIndex]]) »).
22.2.7.8 MakeMatchIndicesIndexPairArray ( S, indices, groupNames, hasGroups )
The abstract operation MakeMatchIndicesIndexPairArray takes arguments S (a
String), indices (a
- Let n be the number of elements in indices.
Assert : n < 232 - 1.Assert : groupNames has n - 1 elements.- NOTE: The groupNames
List contains elements aligned with the indicesList starting at indices[1]. - Let A be !
ArrayCreate (n). - If hasGroups is
true , then- Let groups be
OrdinaryObjectCreate (null ).
- Let groups be
- Else,
- Let groups be
undefined .
- Let groups be
- Perform !
CreateDataPropertyOrThrow (A,"groups" , groups). - For each
integer i such that 0 ≤ i < n, in ascending order, do- Let matchIndices be indices[i].
- If matchIndices is not
undefined , then- Let matchIndexPair be
GetMatchIndexPair (S, matchIndices).
- Let matchIndexPair be
- Else,
- Let matchIndexPair be
undefined .
- Let matchIndexPair be
- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (i)), matchIndexPair). - If i > 0, then
- Let s be groupNames[i - 1].
- If s is not
undefined , thenAssert : groups is notundefined .- NOTE: If there are multiple groups named s,
groups may already have an s property
at this point. However, because groups is an
ordinary object whose properties are all writabledata properties , the call toCreateDataPropertyOrThrow is nevertheless guaranteed to succeed. - Perform !
CreateDataPropertyOrThrow (groups, s, matchIndexPair).
- Return A.
22.2.8 Properties of RegExp Instances
RegExp instances are
Prior to ECMAScript 2015, RegExp instances were specified as having the own RegExp.prototype.
RegExp instances also have the following property:
22.2.8.1 lastIndex
The value of the
22.2.9 RegExp String Iterator Objects
A RegExp String Iterator is an object that represents a specific iteration
over some specific String instance object, matching against some specific RegExp instance
object. There is not a named
22.2.9.1 CreateRegExpStringIterator ( R, S, global, fullUnicode )
The abstract operation CreateRegExpStringIterator takes arguments R (an Object), S (a String), global (a Boolean), and fullUnicode (a Boolean) and returns an Object. It performs the following steps when called:
- Let iterator be
OrdinaryObjectCreate (%RegExpStringIteratorPrototype% , « [[IteratingRegExp]], [[IteratedString]], [[Global]], [[Unicode]], [[Done]] »). - Set iterator.[[IteratingRegExp]] to R.
- Set iterator.[[IteratedString]] to S.
- Set iterator.[[Global]] to global.
- Set iterator.[[Unicode]] to fullUnicode.
- Set iterator.[[Done]] to
false . - Return iterator.
22.2.9.2 The %RegExpStringIteratorPrototype% Object
The %RegExpStringIteratorPrototype% object:
- has properties that are inherited by all
RegExp String Iterator objects . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Iterator.prototype% . - has the following properties:
22.2.9.2.1 %RegExpStringIteratorPrototype%.next ( )
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - If O does not have all of the internal slots of a
RegExp String Iterator Object Instance (see22.2.9.3 ), throw aTypeError exception. - If O.[[Done]] is
true , then- Return
CreateIteratorResultObject (undefined ,true ).
- Return
- Let R be O.[[IteratingRegExp]].
- Let S be O.[[IteratedString]].
- Let global be O.[[Global]].
- Let fullUnicode be O.[[Unicode]].
- Let match be ?
RegExpExec (R, S). - If match is
null , then- Set O.[[Done]] to
true . - Return
CreateIteratorResultObject (undefined ,true ).
- Set O.[[Done]] to
- If global is
false , then- Set O.[[Done]] to
true . - Return
CreateIteratorResultObject (match,false ).
- Set O.[[Done]] to
- Let matchStr be ?
ToString (?Get (match,"0" )). - If matchStr is the empty String, then
- Return
CreateIteratorResultObject (match,false ).
22.2.9.2.2 %RegExpStringIteratorPrototype% [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
22.2.9.3 Properties of RegExp String Iterator Instances
| Internal Slot | Type | Description |
|---|---|---|
| [[IteratingRegExp]] | an Object | The regular expression used for iteration. |
| [[IteratedString]] | a String | The String value being iterated upon. |
| [[Global]] | a Boolean | Indicates whether the [[IteratingRegExp]] is global or not. |
| [[Unicode]] | a Boolean | Indicates whether the [[IteratingRegExp]] is in Unicode mode or not. |
| [[Done]] | a Boolean | Indicates whether the iteration is complete or not. |
23 Indexed Collections
23.1 Array Objects
Arrays are
23.1.1 The Array Constructor
The Array
- is %Array%.
- is the initial value of the
"Array" property of theglobal object . - creates and initializes a new Array when called as a
constructor . - also creates and initializes a new Array when called as a function rather than as a
constructor . Thus the function callArray(…)is equivalent to the object creation expressionnew Array(…)with the same arguments. - is a function whose behaviour differs based upon the number and types of its arguments.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the exotic Array behaviour must include asupercall to the Arrayconstructor to initialize subclass instances that areArray exotic objects . However, most of theArray.prototypemethods are generic methods that are not dependent upon theirthis value being anArray exotic object .
23.1.1.1 Array ( ...values )
This function performs the following steps when called:
- If NewTarget is
undefined , let newTarget be theactive function object ; else let newTarget be NewTarget. - Let proto be ?
GetPrototypeFromConstructor (newTarget,"%Array.prototype%" ). - Let numberOfArgs be the number of elements in values.
- If numberOfArgs = 0, then
- Return !
ArrayCreate (0, proto).
- Return !
- Else if numberOfArgs = 1, then
- Let len be values[0].
- Let array be !
ArrayCreate (0, proto). - If len
is not a Number , then- Perform !
CreateDataPropertyOrThrow (array,"0" , len). - Let intLen be
1 𝔽.
- Perform !
- Else,
- Let intLen be !
ToUint32 (len). - If
SameValueZero (intLen, len) isfalse , throw aRangeError exception.
- Let intLen be !
- Perform !
Set (array,"length" , intLen,true ). - Return array.
- Else,
Assert : numberOfArgs ≥ 2.- Let array be ?
ArrayCreate (numberOfArgs, proto). - Let k be 0.
- Repeat, while k < numberOfArgs,
- Let Pk be !
ToString (𝔽 (k)). - Let itemK be values[k].
- Perform !
CreateDataPropertyOrThrow (array, Pk, itemK). - Set k to k + 1.
- Let Pk be !
Assert : Themathematical value of array's"length" property is numberOfArgs.- Return array.
23.1.2 Properties of the Array Constructor
The Array
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"length" property whose value is1 𝔽. - has the following properties:
23.1.2.1 Array.from ( items [ , mapper [ , thisArg ] ] )
This method performs the following steps when called:
- Let C be the
this value. - If mapper is
undefined , then- Let mapping be
false .
- Let mapping be
- Else,
- If
IsCallable (mapper) isfalse , throw aTypeError exception. - Let mapping be
true .
- If
- Let usingIterator be ?
GetMethod (items,%Symbol.iterator% ). - If usingIterator is not
undefined , then- If
IsConstructor (C) istrue , then- Let A be ?
Construct (C).
- Let A be ?
- Else,
- Let A be !
ArrayCreate (0).
- Let A be !
- Let iteratorRecord be ?
GetIteratorFromMethod (items, usingIterator). - Let k be 0.
- Repeat,
- If k ≥ 253 - 1, then
- Let error be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iteratorRecord, error).
- Let error be
- Let Pk be !
ToString (𝔽 (k)). - Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , then - If mapping is
true , then- Let mappedValue be
Completion (Call (mapper, thisArg, « next,𝔽 (k) »)). IfAbruptCloseIterator (mappedValue, iteratorRecord).
- Let mappedValue be
- Else,
- Let mappedValue be next.
- Let defineStatus be
Completion (CreateDataPropertyOrThrow (A, Pk, mappedValue)). IfAbruptCloseIterator (defineStatus, iteratorRecord).- Set k to k + 1.
- If k ≥ 253 - 1, then
- If
- NOTE: items is not
iterable so assume it is anarray-like object . - Let arrayLike be !
ToObject (items). - Let len be ?
LengthOfArrayLike (arrayLike). - If
IsConstructor (C) istrue , then - Else,
- Let A be ?
ArrayCreate (len).
- Let A be ?
- Let k be 0.
- Repeat, while k < len,
- Perform ?
Set (A,"length" ,𝔽 (len),true ). - Return A.
This method is an intentionally generic factory method; it does not require that its
23.1.2.2 Array.isArray ( arg )
This function performs the following steps when called:
- Return ?
IsArray (arg).
23.1.2.3 Array.of ( ...items )
This method performs the following steps when called:
- Let len be the number of elements in items.
- Let lenNumber be
𝔽 (len). - Let C be the
this value. - If
IsConstructor (C) istrue , then- Let A be ?
Construct (C, « lenNumber »).
- Let A be ?
- Else,
- Let A be ?
ArrayCreate (len).
- Let A be ?
- Let k be 0.
- Repeat, while k < len,
- Let kValue be items[k].
- Let Pk be !
ToString (𝔽 (k)). - Perform ?
CreateDataPropertyOrThrow (A, Pk, kValue). - Set k to k + 1.
- Perform ?
Set (A,"length" , lenNumber,true ). - Return A.
This method is an intentionally generic factory method; it does not require that its
23.1.2.4 Array.prototype
The value of Array.prototype is the
This property has the attributes { [[Writable]]:
23.1.2.5 get Array [ %Symbol.species% ]
Array[%Symbol.species%] is an
- Return the
this value.
The value of the
Array prototype methods normally use their
23.1.3 Properties of the Array Prototype Object
The Array prototype object:
- is %Array.prototype%.
- is an
Array exotic object and has the internal methods specified for such objects. - has a
"length" property whose initial value is+0 𝔽 and whose attributes are { [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }. - has a [[Prototype]] internal slot whose value is
%Object.prototype% .
The Array prototype object is specified to be an
23.1.3.1 Array.prototype.at ( index )
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let relativeIndex be ?
ToIntegerOrInfinity (index). - If relativeIndex ≥ 0, then
- Let k be relativeIndex.
- Else,
- Let k be len + relativeIndex.
- If k < 0 or k ≥ len, return
undefined . - Return ?
Get (O, !ToString (𝔽 (k))).
23.1.3.2 Array.prototype.concat ( ...items )
This method returns an array containing the array elements of the object followed by the array elements of each argument.
It performs the following steps when called:
- Let O be ?
ToObject (this value). - Let A be ?
ArraySpeciesCreate (O, 0). - Let n be 0.
- Prepend O to items.
- For each element E of items, do
- Let spreadable be ?
IsConcatSpreadable (E). - If spreadable is
true , then- Let len be ?
LengthOfArrayLike (E). - If n + len > 253 - 1, throw a
TypeError exception. - Let k be 0.
- Repeat, while k < len,
- Let Pk be !
ToString (𝔽 (k)). - Let exists be ?
HasProperty (E, Pk). - If exists is
true , then- Let subElement be ?
Get (E, Pk). - Perform ?
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), subElement).
- Let subElement be ?
- Set n to n + 1.
- Set k to k + 1.
- Let Pk be !
- Let len be ?
- Else,
- NOTE: E is added as a single item rather than spread.
- If n ≥ 253 - 1, throw a
TypeError exception. - Perform ?
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), E). - Set n to n + 1.
- Let spreadable be ?
- Perform ?
Set (A,"length" ,𝔽 (n),true ). - Return A.
The
The explicit setting of the
This method is intentionally generic; it does not require that its
23.1.3.2.1 IsConcatSpreadable ( O )
The abstract operation IsConcatSpreadable takes argument O (an
- If O
is not an Object , returnfalse . - Let spreadable be ?
Get (O,%Symbol.isConcatSpreadable% ). - If spreadable is not
undefined , returnToBoolean (spreadable). - Return ?
IsArray (O).
23.1.3.3 Array.prototype.constructor
The initial value of Array.prototype.constructor is
23.1.3.4 Array.prototype.copyWithin ( target, start [ , end ] )
The end argument is optional. If it is not provided, the length of the
If target is negative, it is treated as
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let relativeTarget be ?
ToIntegerOrInfinity (target). - If relativeTarget = -∞, let to be 0.
- Else if relativeTarget < 0, let to be
max (len + relativeTarget, 0). - Else, let to be
min (relativeTarget, len). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let from be 0.
- Else if relativeStart < 0, let from be
max (len + relativeStart, 0). - Else, let from be
min (relativeStart, len). - If end is
undefined , let relativeEnd be len; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let final be 0.
- Else if relativeEnd < 0, let final be
max (len + relativeEnd, 0). - Else, let final be
min (relativeEnd, len). - Let count be
min (final - from, len - to). - If from < to and to < from +
count, then
- Let direction be -1.
- Set from to from + count - 1.
- Set to to to + count - 1.
- Else,
- Let direction be 1.
- Repeat, while count > 0,
- Let fromKey be !
ToString (𝔽 (from)). - Let toKey be !
ToString (𝔽 (to)). - Let fromPresent be ?
HasProperty (O, fromKey). - If fromPresent is
true , then - Else,
Assert : fromPresent isfalse .- Perform ?
DeletePropertyOrThrow (O, toKey).
- Set from to from + direction.
- Set to to to + direction.
- Set count to count - 1.
- Let fromKey be !
- Return O.
This method is intentionally generic; it does not require that its
23.1.3.5 Array.prototype.entries ( )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Return
CreateArrayIterator (O,key+value ).
23.1.3.6 Array.prototype.every ( callback [ , thisArg ] )
callback should be a function that accepts three arguments and returns a
value that is coercible to a Boolean value. every calls
callback once for each element present in the array, in ascending order,
until it finds one where callback returns every immediately returns
every returns
If a thisArg parameter is provided, it will be used as the
callback is called with three arguments: the value of the element, the index of the element, and the object being traversed.
every does not directly mutate the object on which it is called but the
object may be mutated by the calls to callback.
The range of elements processed by every is set before the first call to
callback. Elements which are appended to the array after the call to
every begins will not be visited by callback. If existing
elements of the array are changed, their value as passed to callback will
be the value at the time every visits them; elements that are deleted
after the call to every begins and before being visited are not
visited. every acts like the "for all" quantifier in mathematics. In
particular, for an empty array, it returns
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If
IsCallable (callback) isfalse , throw aTypeError exception. - Let k be 0.
- Repeat, while k < len,
- Return
true .
This method is intentionally generic; it does not require that its
23.1.3.7 Array.prototype.fill ( value [ , start [ , end ] ] )
The start argument is optional. If it is not provided,
The end argument is optional. If it is not provided, the length of the
If start is negative, it is treated as
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let k be 0.
- Else if relativeStart < 0, let k be
max (len + relativeStart, 0). - Else, let k be
min (relativeStart, len). - If end is
undefined , let relativeEnd be len; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let final be 0.
- Else if relativeEnd < 0, let final be
max (len + relativeEnd, 0). - Else, let final be
min (relativeEnd, len). - Repeat, while k < final,
- Return O.
This method is intentionally generic; it does not require that its
23.1.3.8 Array.prototype.filter ( callback [ , thisArg ] )
callback should be a function that accepts three arguments and returns a
value that is coercible to a Boolean value. filter calls
callback once for each element in the array, in ascending order, and
constructs a new array of all the values for which callback returns
If a thisArg parameter is provided, it will be used as the
callback is called with three arguments: the value of the element, the index of the element, and the object being traversed.
filter does not directly mutate the object on which it is called but the
object may be mutated by the calls to callback.
The range of elements processed by filter is set before the first call
to callback. Elements which are appended to the array after the call to
filter begins will not be visited by callback. If existing
elements of the array are changed their value as passed to callback will
be the value at the time filter visits them; elements that are deleted
after the call to filter begins and before being visited are not
visited.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If
IsCallable (callback) isfalse , throw aTypeError exception. - Let A be ?
ArraySpeciesCreate (O, 0). - Let k be 0.
- Let to be 0.
- Repeat, while k < len,
- Let Pk be !
ToString (𝔽 (k)). - Let kPresent be ?
HasProperty (O, Pk). - If kPresent is
true , then - Set k to k + 1.
- Let Pk be !
- Return A.
This method is intentionally generic; it does not require that its
23.1.3.9 Array.prototype.find ( predicate [ , thisArg ] )
This method calls predicate once for each element of the array, in
ascending index order, until it finds one where predicate returns a value
that coerces to find immediately returns that element value. Otherwise,
find returns
See
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let findRec be ?
FindViaPredicate (O, len,ascending , predicate, thisArg). - Return findRec.[[Value]].
This method is intentionally generic; it does not require that its
23.1.3.10 Array.prototype.findIndex ( predicate [ , thisArg ] )
This method calls predicate once for each element of the array, in
ascending index order, until it finds one where predicate returns a value
that coerces to findIndex immediately returns the index of that element value.
Otherwise, findIndex returns -1.
See
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let findRec be ?
FindViaPredicate (O, len,ascending , predicate, thisArg). - Return findRec.[[Index]].
This method is intentionally generic; it does not require that its
23.1.3.11 Array.prototype.findLast ( predicate [ , thisArg ] )
This method calls predicate once for each element of the array, in
descending index order, until it finds one where predicate returns a
value that coerces to findLast immediately returns that element value. Otherwise,
findLast returns
See
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let findRec be ?
FindViaPredicate (O, len,descending , predicate, thisArg). - Return findRec.[[Value]].
This method is intentionally generic; it does not require that its
23.1.3.12 Array.prototype.findLastIndex ( predicate [ , thisArg ] )
This method calls predicate once for each element of the array, in
descending index order, until it finds one where predicate returns a
value that coerces to findLastIndex immediately returns the index of that element value.
Otherwise, findLastIndex returns -1.
See
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let findRec be ?
FindViaPredicate (O, len,descending , predicate, thisArg). - Return findRec.[[Index]].
This method is intentionally generic; it does not require that its
23.1.3.12.1 FindViaPredicate ( O, len, direction, predicate, thisArg )
The abstract operation FindViaPredicate takes arguments O (an Object),
len (a non-negative
O should be an
predicate should be a function. When called for an element of the array, it is passed three arguments: the value of the element, the index of the element, and the object being traversed. Its return value will be coerced to a Boolean value.
thisArg will be used as the
This operation does not directly mutate the object on which it is called, but the object may be mutated by the calls to predicate.
The range of elements processed is set before the first call to predicate,
just before the traversal begins. Elements that are appended to the array after this
will not be visited by predicate. If existing elements of the array are
changed, their value as passed to predicate will be the value at the time
that this operation visits them. Elements that are deleted after traversal begins and
before being visited are still visited and are either looked up from the prototype or
are
It performs the following steps when called:
- If
IsCallable (predicate) isfalse , throw aTypeError exception. - If direction is
ascending , then - Else,
- For each
integer k of indices, do- Let Pk be !
ToString (𝔽 (k)). - NOTE: If O is a
TypedArray , the following invocation ofGet will return anormal completion . - Let kValue be ?
Get (O, Pk). - Let testResult be ?
Call (predicate, thisArg, « kValue,𝔽 (k), O »). - If
ToBoolean (testResult) istrue , return theRecord { [[Index]]:𝔽 (k), [[Value]]: kValue }.
- Let Pk be !
- Return the
Record { [[Index]]:-1 𝔽, [[Value]]:undefined }.
23.1.3.13 Array.prototype.flat ( [ depth ] )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let sourceLen be ?
LengthOfArrayLike (O). - Let depthNum be 1.
- If depth is not
undefined , then- Set depthNum to ?
ToIntegerOrInfinity (depth). - If depthNum < 0, set depthNum to 0.
- Set depthNum to ?
- Let A be ?
ArraySpeciesCreate (O, 0). - Perform ?
FlattenIntoArray (A, O, sourceLen, 0, depthNum). - Return A.
23.1.3.13.1 FlattenIntoArray ( target, source, sourceLen, start, depth [ , mapperFunction [ , thisArg ] ] )
The abstract operation FlattenIntoArray takes arguments target (an Object),
source (an Object), sourceLen (a non-negative
Assert : If mapperFunction is present, thenIsCallable (mapperFunction) istrue , thisArg is present, and depth is 1.- Let targetIndex be start.
- Let sourceIndex be
+0 𝔽. - Repeat, while
ℝ (sourceIndex) < sourceLen,- Let P be !
ToString (sourceIndex). - Let exists be ?
HasProperty (source, P). - If exists is
true , then- Let element be ?
Get (source, P). - If mapperFunction is present, then
- Set element to ?
Call (mapperFunction, thisArg, « element, sourceIndex, source »).
- Set element to ?
- Let shouldFlatten be
false . - If depth > 0, then
- Set shouldFlatten to ?
IsArray (element).
- Set shouldFlatten to ?
- If shouldFlatten is
true , then- If depth = +∞, let newDepth be +∞.
- Else, let newDepth be depth - 1.
- Let elementLen be ?
LengthOfArrayLike (element). - Set targetIndex to ?
FlattenIntoArray (target, element, elementLen, targetIndex, newDepth).
- Else,
- If targetIndex ≥ 253 - 1, throw a
TypeError exception. - Perform ?
CreateDataPropertyOrThrow (target, !ToString (𝔽 (targetIndex)), element). - Set targetIndex to targetIndex + 1.
- If targetIndex ≥ 253 - 1, throw a
- Let element be ?
- Set sourceIndex to sourceIndex +
1 𝔽.
- Let P be !
- Return targetIndex.
23.1.3.14 Array.prototype.flatMap ( mapperFunction [ , thisArg ] )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let sourceLen be ?
LengthOfArrayLike (O). - If
IsCallable (mapperFunction) isfalse , throw aTypeError exception. - Let A be ?
ArraySpeciesCreate (O, 0). - Perform ?
FlattenIntoArray (A, O, sourceLen, 0, 1, mapperFunction, thisArg). - Return A.
23.1.3.15 Array.prototype.forEach ( callback [ , thisArg ] )
callback should be a function that accepts three arguments.
forEach calls callback once for each element present in the
array, in ascending order. callback is called only for elements of the
array which actually exist; it is not called for missing elements of the array.
If a thisArg parameter is provided, it will be used as the
callback is called with three arguments: the value of the element, the index of the element, and the object being traversed.
forEach does not directly mutate the object on which it is called but
the object may be mutated by the calls to callback.
The range of elements processed by forEach is set before the first call
to callback. Elements which are appended to the array after the call to
forEach begins will not be visited by callback. If existing
elements of the array are changed, their value as passed to callback will
be the value at the time forEach visits them; elements that are deleted
after the call to forEach begins and before being visited are not
visited.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If
IsCallable (callback) isfalse , throw aTypeError exception. - Let k be 0.
- Repeat, while k < len,
- Return
undefined .
This method is intentionally generic; it does not require that its
23.1.3.16 Array.prototype.includes ( searchElement [ , fromIndex ] )
This method compares searchElement to the elements of the array, in
ascending order, using the
The optional second argument fromIndex defaults to
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If len = 0, return
false . - Let n be ?
ToIntegerOrInfinity (fromIndex). Assert : If fromIndex isundefined , then n is 0.- If n = +∞, return
false . - Else if n = -∞, set n to 0.
- If n ≥ 0, then
- Let k be n.
- Else,
- Let k be len + n.
- If k < 0, set k to 0.
- Repeat, while k < len,
- Let elementK be ?
Get (O, !ToString (𝔽 (k))). - If
SameValueZero (searchElement, elementK) istrue , returntrue . - Set k to k + 1.
- Let elementK be ?
- Return
false .
This method is intentionally generic; it does not require that its
This method intentionally differs from the similar indexOf method in two
ways. First, it uses the
23.1.3.17 Array.prototype.indexOf ( searchElement [ , fromIndex ] )
This method compares searchElement to the elements of the array, in ascending
order, using the
The optional second argument fromIndex defaults to
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If len = 0, return
-1 𝔽. - Let n be ?
ToIntegerOrInfinity (fromIndex). Assert : If fromIndex isundefined , then n is 0.- If n = +∞, return
-1 𝔽. - Else if n = -∞, set n to 0.
- If n ≥ 0, then
- Let k be n.
- Else,
- Let k be len + n.
- If k < 0, set k to 0.
- Repeat, while k < len,
- Let Pk be !
ToString (𝔽 (k)). - Let kPresent be ?
HasProperty (O, Pk). - If kPresent is
true , then- Let elementK be ?
Get (O, Pk). - If
IsStrictlyEqual (searchElement, elementK) istrue , return𝔽 (k).
- Let elementK be ?
- Set k to k + 1.
- Let Pk be !
- Return
-1 𝔽.
This method is intentionally generic; it does not require that its
23.1.3.18 Array.prototype.join ( separator )
This method converts the elements of the array to Strings, and then concatenates these Strings, separated by occurrences of the separator. If no separator is provided, a single comma is used as the separator.
It performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If separator is
undefined , let sep be"," . - Else, let sep be ?
ToString (separator). - Let R be the empty String.
- Let k be 0.
- Repeat, while k < len,
- If k > 0, set R to the
string-concatenation of R and sep. - Let element be ?
Get (O, !ToString (𝔽 (k))). - If element is neither
undefined nornull , then- Let S be ?
ToString (element). - Set R to the
string-concatenation of R and S.
- Let S be ?
- Set k to k + 1.
- If k > 0, set R to the
- Return R.
This method is intentionally generic; it does not require that its
23.1.3.19 Array.prototype.keys ( )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Return
CreateArrayIterator (O,key ).
23.1.3.20 Array.prototype.lastIndexOf ( searchElement [ , fromIndex ] )
This method compares searchElement to the elements of the array in
descending order using the
The optional second argument fromIndex defaults to the array's length
minus one (i.e. the whole array is searched). If it is greater than or equal to the
length of the array, the whole array will be searched. If it is less than
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If len = 0, return
-1 𝔽. - If fromIndex is present, let n be ?
ToIntegerOrInfinity (fromIndex); else let n be len - 1. - If n = -∞, return
-1 𝔽. - If n ≥ 0, then
- Let k be
min (n, len - 1).
- Let k be
- Else,
- Let k be len + n.
- Repeat, while k ≥ 0,
- Let Pk be !
ToString (𝔽 (k)). - Let kPresent be ?
HasProperty (O, Pk). - If kPresent is
true , then- Let elementK be ?
Get (O, Pk). - If
IsStrictlyEqual (searchElement, elementK) istrue , return𝔽 (k).
- Let elementK be ?
- Set k to k - 1.
- Let Pk be !
- Return
-1 𝔽.
This method is intentionally generic; it does not require that its
23.1.3.21 Array.prototype.map ( callback [ , thisArg ] )
callback should be a function that accepts three arguments.
map calls callback once for each element in the array, in
ascending order, and constructs a new Array from the results. callback is
called only for elements of the array which actually exist; it is not called for
missing elements of the array.
If a thisArg parameter is provided, it will be used as the
callback is called with three arguments: the value of the element, the index of the element, and the object being traversed.
map does not directly mutate the object on which it is called but the
object may be mutated by the calls to callback.
The range of elements processed by map is set before the first call to
callback. Elements which are appended to the array after the call to
map begins will not be visited by callback. If existing
elements of the array are changed, their value as passed to callback will
be the value at the time map visits them; elements that are deleted
after the call to map begins and before being visited are not visited.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If
IsCallable (callback) isfalse , throw aTypeError exception. - Let A be ?
ArraySpeciesCreate (O, len). - Let k be 0.
- Repeat, while k < len,
- Let Pk be !
ToString (𝔽 (k)). - Let kPresent be ?
HasProperty (O, Pk). - If kPresent is
true , then- Let kValue be ?
Get (O, Pk). - Let mappedValue be ?
Call (callback, thisArg, « kValue,𝔽 (k), O »). - Perform ?
CreateDataPropertyOrThrow (A, Pk, mappedValue).
- Let kValue be ?
- Set k to k + 1.
- Let Pk be !
- Return A.
This method is intentionally generic; it does not require that its
23.1.3.22 Array.prototype.pop ( )
This method removes the last element of the array and returns it.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If len = 0, then
- Perform ?
Set (O,"length" ,+0 𝔽,true ). - Return
undefined .
- Perform ?
- Else,
This method is intentionally generic; it does not require that its
23.1.3.23 Array.prototype.push ( ...items )
This method appends the arguments to the end of the array, in the order in which they appear. It returns the new length of the array.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let argCount be the number of elements in items.
- If len + argCount > 253 - 1, throw a
TypeError exception. - For each element E of items, do
- Perform ?
Set (O,"length" ,𝔽 (len),true ). - Return
𝔽 (len).
The
This method is intentionally generic; it does not require that its
23.1.3.24 Array.prototype.reduce ( callback [ , initialValue ] )
callback should be a function that takes four arguments.
reduce calls the callback, as a function, once for each element after
the first element present in the array, in ascending order.
callback is called with four arguments: the previousValue
(value from the previous call to callback), the currentValue
(value of the current element), the currentIndex, and the object being
traversed. The first time that callback is called, the previousValue and
currentValue can be one of two values. If an initialValue was
supplied in the call to reduce, then previousValue will be
initialValue and currentValue will be the first value in the
array. If no initialValue was supplied, then previousValue
will be the first value in the array and currentValue will be the second.
It is a
reduce does not directly mutate the object on which it is called but the
object may be mutated by the calls to callback.
The range of elements processed by reduce is set before the first call
to callback. Elements that are appended to the array after the call to
reduce begins will not be visited by callback. If existing
elements of the array are changed, their value as passed to callback will
be the value at the time reduce visits them; elements that are deleted
after the call to reduce begins and before being visited are not
visited.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If
IsCallable (callback) isfalse , throw aTypeError exception. - If len = 0 and initialValue is not present, throw a
TypeError exception. - Let k be 0.
- Let accumulator be
undefined . - If initialValue is present, then
- Set accumulator to initialValue.
- Else,
- Let kPresent be
false . - Repeat, while kPresent is
false and k < len,- Let Pk be !
ToString (𝔽 (k)). - Set kPresent to ?
HasProperty (O, Pk). - If kPresent is
true , then- Set accumulator to ?
Get (O, Pk).
- Set accumulator to ?
- Set k to k + 1.
- Let Pk be !
- If kPresent is
false , throw aTypeError exception.
- Let kPresent be
- Repeat, while k < len,
- Return accumulator.
This method is intentionally generic; it does not require that its
23.1.3.25 Array.prototype.reduceRight ( callback [ , initialValue ] )
callback should be a function that takes four arguments.
reduceRight calls the callback, as a function, once for each element
after the first element present in the array, in descending order.
callback is called with four arguments: the previousValue
(value from the previous call to callback), the currentValue
(value of the current element), the currentIndex, and the object being
traversed. The first time the function is called, the previousValue and
currentValue can be one of two values. If an initialValue was
supplied in the call to reduceRight, then previousValue will
be initialValue and currentValue will be the last value in the
array. If no initialValue was supplied, then previousValue
will be the last value in the array and currentValue will be the
second-to-last value. It is a
reduceRight does not directly mutate the object on which it is called
but the object may be mutated by the calls to callback.
The range of elements processed by reduceRight is set before the first
call to callback. Elements that are appended to the array after the call
to reduceRight begins will not be visited by callback. If
existing elements of the array are changed by callback, their value as
passed to callback will be the value at the time reduceRight
visits them; elements that are deleted after the call to reduceRight
begins and before being visited are not visited.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If
IsCallable (callback) isfalse , throw aTypeError exception. - If len = 0 and initialValue is not present, throw a
TypeError exception. - Let k be len - 1.
- Let accumulator be
undefined . - If initialValue is present, then
- Set accumulator to initialValue.
- Else,
- Let kPresent be
false . - Repeat, while kPresent is
false and k ≥ 0,- Let Pk be !
ToString (𝔽 (k)). - Set kPresent to ?
HasProperty (O, Pk). - If kPresent is
true , then- Set accumulator to ?
Get (O, Pk).
- Set accumulator to ?
- Set k to k - 1.
- Let Pk be !
- If kPresent is
false , throw aTypeError exception.
- Let kPresent be
- Repeat, while k ≥ 0,
- Return accumulator.
This method is intentionally generic; it does not require that its
23.1.3.26 Array.prototype.reverse ( )
This method rearranges the elements of the array so as to reverse their order. It returns the reversed array.
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let middle be
floor (len / 2). - Let lower be 0.
- Repeat, while lower ≠ middle,
- Let upper be len - lower - 1.
- Let upperP be !
ToString (𝔽 (upper)). - Let lowerP be !
ToString (𝔽 (lower)). - Let lowerExists be ?
HasProperty (O, lowerP). - If lowerExists is
true , then- Let lowerValue be ?
Get (O, lowerP).
- Let lowerValue be ?
- Let upperExists be ?
HasProperty (O, upperP). - If upperExists is
true , then- Let upperValue be ?
Get (O, upperP).
- Let upperValue be ?
- If lowerExists is
true and upperExists istrue , then - Else if lowerExists is
false and upperExists istrue , then- Perform ?
Set (O, lowerP, upperValue,true ). - Perform ?
DeletePropertyOrThrow (O, upperP).
- Perform ?
- Else if lowerExists is
true and upperExists isfalse , then- Perform ?
DeletePropertyOrThrow (O, lowerP). - Perform ?
Set (O, upperP, lowerValue,true ).
- Perform ?
- Else,
Assert : lowerExists and upperExists are bothfalse .- NOTE: No action is required.
- Set lower to lower + 1.
- Return O.
This method is intentionally generic; it does not require that its
23.1.3.27 Array.prototype.shift ( )
This method removes the first element of the array and returns it.
It performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If len = 0, then
- Perform ?
Set (O,"length" ,+0 𝔽,true ). - Return
undefined .
- Perform ?
- Let first be ?
Get (O,"0" ). - Let k be 1.
- Repeat, while k < len,
- Let from be !
ToString (𝔽 (k)). - Let to be !
ToString (𝔽 (k - 1)). - Let fromPresent be ?
HasProperty (O, from). - If fromPresent is
true , then - Else,
Assert : fromPresent isfalse .- Perform ?
DeletePropertyOrThrow (O, to).
- Set k to k + 1.
- Let from be !
- Perform ?
DeletePropertyOrThrow (O, !ToString (𝔽 (len - 1))). - Perform ?
Set (O,"length" ,𝔽 (len - 1),true ). - Return first.
This method is intentionally generic; it does not require that its
23.1.3.28 Array.prototype.slice ( start, end )
This method returns an array containing the elements of the array from element
start up to, but not including, element end (or through the end of the
array if end is
It performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let k be 0.
- Else if relativeStart < 0, let k be
max (len + relativeStart, 0). - Else, let k be
min (relativeStart, len). - If end is
undefined , let relativeEnd be len; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let final be 0.
- Else if relativeEnd < 0, let final be
max (len + relativeEnd, 0). - Else, let final be
min (relativeEnd, len). - Let count be
max (final - k, 0). - Let A be ?
ArraySpeciesCreate (O, count). - Let n be 0.
- Repeat, while k < final,
- Let Pk be !
ToString (𝔽 (k)). - Let kPresent be ?
HasProperty (O, Pk). - If kPresent is
true , then- Let kValue be ?
Get (O, Pk). - Perform ?
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), kValue).
- Let kValue be ?
- Set k to k + 1.
- Set n to n + 1.
- Let Pk be !
- Perform ?
Set (A,"length" ,𝔽 (n),true ). - Return A.
The explicit setting of the
This method is intentionally generic; it does not require that its
23.1.3.29 Array.prototype.some ( callback [ , thisArg ] )
callback should be a function that accepts three arguments and returns a
value that is coercible to a Boolean value. some calls
callback once for each element present in the array, in ascending order,
until it finds one where callback returns some immediately returns
some returns
If a thisArg parameter is provided, it will be used as the
callback is called with three arguments: the value of the element, the index of the element, and the object being traversed.
some does not directly mutate the object on which it is called but the
object may be mutated by the calls to callback.
The range of elements processed by some is set before the first call to
callback. Elements that are appended to the array after the call to
some begins will not be visited by callback. If existing
elements of the array are changed, their value as passed to callback will
be the value at the time that some visits them; elements that are
deleted after the call to some begins and before being visited are not
visited. some acts like the "exists" quantifier in mathematics. In
particular, for an empty array, it returns
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - If
IsCallable (callback) isfalse , throw aTypeError exception. - Let k be 0.
- Repeat, while k < len,
- Return
false .
This method is intentionally generic; it does not require that its
23.1.3.30 Array.prototype.sort ( comparator )
This method sorts the elements of this array. If comparator is not
It performs the following steps when called:
- If comparator is not
undefined andIsCallable (comparator) isfalse , throw aTypeError exception. - Let obj be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (obj). - Let SortCompare be a new
Abstract Closure with parameters (x, y) that captures comparator and performs the following steps when called:- Return ?
CompareArrayElements (x, y, comparator).
- Return ?
- Let sortedList be ?
SortIndexedProperties (obj, len, SortCompare,skip-holes ). - Let itemCount be the number of elements in sortedList.
- Let j be 0.
- Repeat, while j < itemCount,
- NOTE: The call to
SortIndexedProperties in step5 usesskip-holes . The remaining indices are deleted to preserve the number of holes that were detected and excluded from the sort. - Repeat, while j < len,
- Perform ?
DeletePropertyOrThrow (obj, !ToString (𝔽 (j))). - Set j to j + 1.
- Perform ?
- Return obj.
Because non-existent property values always compare greater than
Method calls performed by the
This method is intentionally generic; it does not require that its
23.1.3.30.1 SortIndexedProperties ( obj, len, SortCompare, holes )
The abstract operation SortIndexedProperties takes arguments obj (an Object),
len (a non-negative
- Let items be a new empty
List . - Let k be 0.
- Repeat, while k < len,
- Let Pk be !
ToString (𝔽 (k)). - If holes is
skip-holes , then- Let kRead be ?
HasProperty (obj, Pk).
- Let kRead be ?
- Else,
Assert : holes isread-through-holes .- Let kRead be
true .
- If kRead is
true , then- Let kValue be ?
Get (obj, Pk). - Append kValue to items.
- Let kValue be ?
- Set k to k + 1.
- Let Pk be !
- Sort items using an
implementation-defined sequence of calls to SortCompare. If any such call returns anabrupt completion , stop before performing any further calls to SortCompare and return thatCompletion Record . - Return items.
The sort order is the ordering of
items after completion of step
Unless the
-
There must be some mathematical permutation π of the non-negative
integers less than itemCount, such that for every non-negativeinteger j less than itemCount, the elementold[j] is exactly the same asnew[π(j)] . -
Then for all non-negative
integers j and k, each less than itemCount, ifℝ (SortCompare(old[j], old[k])) < 0π(j) < π(k) . -
And for all non-negative
integers j and k such that j < k < itemCount, ifℝ (SortCompare(old[j], old[k])) = 0π(j) < π(k) ; i.e., the sort is stable.
Here the notation
An abstract closure or function comparator is a consistent comparator for a set of
values S if all of the requirements below are met for all values
a, b, and c (possibly the same value) in the set
S: The notation
-
Calling comparator(a, b) always returns the same
value v when given a specific pair of values a and
b as its two arguments. Furthermore, v
is a Number , and v is notNaN . Note that this implies that exactly one of a <C b, a =C b, and a >C b will be true for a given pair of a and b. - Calling comparator(a, b) does not modify obj or any object on obj's prototype chain.
- a =C a (reflexivity)
- If a =C b, then b =C a (symmetry)
- If a =C b and b =C c, then a =C c (transitivity of =C)
- If a <C b and b <C c, then a <C c (transitivity of <C)
- If a >C b and b >C c, then a >C c (transitivity of >C)
The above conditions are necessary and sufficient to ensure that comparator divides the set S into equivalence classes and that these equivalence classes are totally ordered.
23.1.3.30.2 CompareArrayElements ( x, y, comparator )
The abstract operation CompareArrayElements takes arguments x (an
- If x and y are both
undefined , return+0 𝔽. - If x is
undefined , return1 𝔽. - If y is
undefined , return-1 𝔽. - If comparator is not
undefined , then - Let xString be ?
ToString (x). - Let yString be ?
ToString (y). - Let xSmaller be !
IsLessThan (xString, yString,true ). - If xSmaller is
true , return-1 𝔽. - Let ySmaller be !
IsLessThan (yString, xString,true ). - If ySmaller is
true , return1 𝔽. - Return
+0 𝔽.
23.1.3.31 Array.prototype.splice ( start, deleteCount, ...items )
This method deletes the deleteCount elements of the array starting at
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let actualStart be 0.
- Else if relativeStart < 0, let actualStart be
max (len + relativeStart, 0). - Else, let actualStart be
min (relativeStart, len). - Let itemCount be the number of elements in items.
- If start is not present, then
- Let actualDeleteCount be 0.
- Else if deleteCount is not present, then
- Let actualDeleteCount be len - actualStart.
- Else,
- Let dc be ?
ToIntegerOrInfinity (deleteCount). - Let actualDeleteCount be the result of
clamping dc between 0 and len - actualStart.
- Let dc be ?
- If len + itemCount - actualDeleteCount >
253 - 1, throw a
TypeError exception. - Let A be ?
ArraySpeciesCreate (O, actualDeleteCount). - Let k be 0.
- Repeat, while k < actualDeleteCount,
- Let from be !
ToString (𝔽 (actualStart + k)). - If ?
HasProperty (O, from) istrue , then- Let fromValue be ?
Get (O, from). - Perform ?
CreateDataPropertyOrThrow (A, !ToString (𝔽 (k)), fromValue).
- Let fromValue be ?
- Set k to k + 1.
- Let from be !
- Perform ?
Set (A,"length" ,𝔽 (actualDeleteCount),true ). - If itemCount < actualDeleteCount, then
- Set k to actualStart.
- Repeat, while k < (len -
actualDeleteCount),
- Let from be !
ToString (𝔽 (k + actualDeleteCount)). - Let to be !
ToString (𝔽 (k + itemCount)). - If ?
HasProperty (O, from) istrue , then - Else,
- Perform ?
DeletePropertyOrThrow (O, to).
- Perform ?
- Set k to k + 1.
- Let from be !
- Set k to len.
- Repeat, while k > (len -
actualDeleteCount + itemCount),
- Perform ?
DeletePropertyOrThrow (O, !ToString (𝔽 (k - 1))). - Set k to k - 1.
- Perform ?
- Else if itemCount > actualDeleteCount, then
- Set k to (len - actualDeleteCount).
- Repeat, while k > actualStart,
- Let from be !
ToString (𝔽 (k + actualDeleteCount - 1)). - Let to be !
ToString (𝔽 (k + itemCount - 1)). - If ?
HasProperty (O, from) istrue , then - Else,
- Perform ?
DeletePropertyOrThrow (O, to).
- Perform ?
- Set k to k - 1.
- Let from be !
- Set k to actualStart.
- For each element E of items, do
- Perform ?
Set (O,"length" ,𝔽 (len - actualDeleteCount + itemCount),true ). - Return A.
This method is intentionally generic; it does not require that its
23.1.3.32 Array.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used.
The first edition of ECMA-402 did not include a replacement specification for this method.
The meanings of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
This method performs the following steps when called:
- Let array be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (array). - Let separator be the
implementation-defined list-separator String value appropriate for thehost environment 's current locale (such as", " ). - Let R be the empty String.
- Let k be 0.
- Repeat, while k < len,
- If k > 0, set R to the
string-concatenation of R and separator. - Let element be ?
Get (array, !ToString (𝔽 (k))). - If element is neither
undefined nornull , then- Let S be ?
ToString (?Invoke (element,"toLocaleString" )). - Set R to the
string-concatenation of R and S.
- Let S be ?
- Set k to k + 1.
- If k > 0, set R to the
- Return R.
This method converts the elements of the array to Strings using their
toLocaleString methods, and then concatenates these Strings, separated
by occurrences of an toString
except that it is intended to yield a locale-sensitive result corresponding with
conventions of the
This method is intentionally generic; it does not require that its
23.1.3.33 Array.prototype.toReversed ( )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let A be ?
ArrayCreate (len). - Let k be 0.
- Repeat, while k < len,
- Return A.
23.1.3.34 Array.prototype.toSorted ( comparator )
This method performs the following steps when called:
- If comparator is not
undefined andIsCallable (comparator) isfalse , throw aTypeError exception. - Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let A be ?
ArrayCreate (len). - Let SortCompare be a new
Abstract Closure with parameters (x, y) that captures comparator and performs the following steps when called:- Return ?
CompareArrayElements (x, y, comparator).
- Return ?
- Let sortedList be ?
SortIndexedProperties (O, len, SortCompare,read-through-holes ). - Let j be 0.
- Repeat, while j < len,
- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (j)), sortedList[j]). - Set j to j + 1.
- Perform !
- Return A.
23.1.3.35 Array.prototype.toSpliced ( start, skipCount, ...items )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let actualStart be 0.
- Else if relativeStart < 0, let actualStart be
max (len + relativeStart, 0). - Else, let actualStart be
min (relativeStart, len). - Let insertCount be the number of elements in items.
- If start is not present, then
- Let actualSkipCount be 0.
- Else if skipCount is not present, then
- Let actualSkipCount be len - actualStart.
- Else,
- Let sc be ?
ToIntegerOrInfinity (skipCount). - Let actualSkipCount be the result of
clamping sc between 0 and len - actualStart.
- Let sc be ?
- Let newLen be len + insertCount - actualSkipCount.
- If newLen > 253 - 1, throw a
TypeError exception. - Let A be ?
ArrayCreate (newLen). - Let i be 0.
- Let r be actualStart + actualSkipCount.
- Repeat, while i < actualStart,
- Let Pi be !
ToString (𝔽 (i)). - Let iValue be ?
Get (O, Pi). - Perform !
CreateDataPropertyOrThrow (A, Pi, iValue). - Set i to i + 1.
- Let Pi be !
- For each element E of items, do
- Let Pi be !
ToString (𝔽 (i)). - Perform !
CreateDataPropertyOrThrow (A, Pi, E). - Set i to i + 1.
- Let Pi be !
- Repeat, while i < newLen,
- Return A.
23.1.3.36 Array.prototype.toString ( )
This method performs the following steps when called:
- Let array be ?
ToObject (this value). - Let func be ?
Get (array,"join" ). - If
IsCallable (func) isfalse , set func to the intrinsic function %Object.prototype.toString%. - Return ?
Call (func, array).
This method is intentionally generic; it does not require that its
23.1.3.37 Array.prototype.unshift ( ...items )
This method prepends the arguments to the start of the array, such that their order within the array is the same as the order in which they appear in the argument list.
It performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let argCount be the number of elements in items.
- If argCount > 0, then
- If len + argCount > 253 - 1, throw a
TypeError exception. - Let k be len.
- Repeat, while k > 0,
- Let from be !
ToString (𝔽 (k - 1)). - Let to be !
ToString (𝔽 (k + argCount - 1)). - Let fromPresent be ?
HasProperty (O, from). - If fromPresent is
true , then - Else,
Assert : fromPresent isfalse .- Perform ?
DeletePropertyOrThrow (O, to).
- Set k to k - 1.
- Let from be !
- Let j be
+0 𝔽. - For each element E of items, do
- If len + argCount > 253 - 1, throw a
- Perform ?
Set (O,"length" ,𝔽 (len + argCount),true ). - Return
𝔽 (len + argCount).
The
This method is intentionally generic; it does not require that its
23.1.3.38 Array.prototype.values ( )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Return
CreateArrayIterator (O,value ).
23.1.3.39 Array.prototype.with ( index, value )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let len be ?
LengthOfArrayLike (O). - Let relativeIndex be ?
ToIntegerOrInfinity (index). - If relativeIndex ≥ 0, let actualIndex be relativeIndex.
- Else, let actualIndex be len + relativeIndex.
- If actualIndex ≥ len or actualIndex < 0, throw a
RangeError exception. - Let A be ?
ArrayCreate (len). - Let k be 0.
- Repeat, while k < len,
- Let Pk be !
ToString (𝔽 (k)). - If k = actualIndex, let fromValue be value.
- Else, let fromValue be ?
Get (O, Pk). - Perform !
CreateDataPropertyOrThrow (A, Pk, fromValue). - Set k to k + 1.
- Let Pk be !
- Return A.
23.1.3.40 Array.prototype [ %Symbol.iterator% ] ( )
The initial value of the
23.1.3.41 Array.prototype [ %Symbol.unscopables% ]
The initial value of the
- Let unscopableList be
OrdinaryObjectCreate (null ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"at" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"copyWithin" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"entries" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"fill" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"find" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"findIndex" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"findLast" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"findLastIndex" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"flat" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"flatMap" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"includes" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"keys" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"toReversed" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"toSorted" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"toSpliced" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"values" ,true ). - Return unscopableList.
This property has the attributes { [[Writable]]:
The own property names of this object are property names that were not included as
standard properties of Array.prototype prior to the ECMAScript 2015
specification. These names are ignored for with statement binding
purposes in order to preserve the behaviour of existing code that might use one of
these names as a binding in an outer scope that is shadowed by a with
statement whose binding object is an Array.
The reason that
23.1.4 Properties of Array Instances
Array instances are
Array instances have a
23.1.4.1 length
The
The
Reducing the value of the
23.1.5 Array Iterator Objects
An Array Iterator is an object that represents a specific iteration over
some specific Array instance object. There is not a named
23.1.5.1 CreateArrayIterator ( array, kind )
The abstract operation CreateArrayIterator takes arguments array (an Object) and
kind (
- Let iterator be
OrdinaryObjectCreate (%ArrayIteratorPrototype% , « [[IteratedArrayLike]], [[ArrayLikeNextIndex]], [[ArrayLikeIterationKind]] »). - Set iterator.[[IteratedArrayLike]] to array.
- Set iterator.[[ArrayLikeNextIndex]] to 0.
- Set iterator.[[ArrayLikeIterationKind]] to kind.
- Return iterator.
23.1.5.2 The %ArrayIteratorPrototype% Object
The %ArrayIteratorPrototype% object:
- has properties that are inherited by all
Array Iterator objects . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Iterator.prototype% . - has the following properties:
23.1.5.2.1 %ArrayIteratorPrototype%.next ( )
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - If O does not have all of the internal slots of an
Array Iterator Instance (23.1.5.3 ), throw aTypeError exception. - Let array be O.[[IteratedArrayLike]].
- If array is
undefined , returnCreateIteratorResultObject (undefined ,true ). - Let index be O.[[ArrayLikeNextIndex]].
- Let kind be O.[[ArrayLikeIterationKind]].
- If array has a [[TypedArrayName]] internal
slot, then
- Let taRecord be
MakeTypedArrayWithBufferWitnessRecord (array,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Let len be
TypedArrayLength (taRecord).
- Let taRecord be
- Else,
- Let len be ?
LengthOfArrayLike (array).
- Let len be ?
- If index ≥ len, then
- Set O.[[IteratedArrayLike]] to
undefined . - Return
CreateIteratorResultObject (undefined ,true ).
- Set O.[[IteratedArrayLike]] to
- Set O.[[ArrayLikeNextIndex]] to index + 1.
- Let indexNumber be
𝔽 (index). - If kind is
key , then- Let result be indexNumber.
- Else,
- Let elementKey be !
ToString (indexNumber). - Let elementValue be ?
Get (array, elementKey). - If kind is
value , then- Let result be elementValue.
- Else,
Assert : kind iskey+value .- Let result be
CreateArrayFromList (« indexNumber, elementValue »).
- Let elementKey be !
- Return
CreateIteratorResultObject (result,false ).
23.1.5.2.2 %ArrayIteratorPrototype% [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
23.1.5.3 Properties of Array Iterator Instances
| Internal Slot | Type | Description |
|---|---|---|
| [[IteratedArrayLike]] |
an Object or |
The |
| [[ArrayLikeNextIndex]] |
a non-negative |
The |
| [[ArrayLikeIterationKind]] |
|
A value that identifies what is returned for each element of the iteration. |
23.2 TypedArray Objects
A TypedArray presents an array-like view of an underlying binary data buffer (
|
|
Element Type | Element Size | Conversion Operation | Description |
|---|---|---|---|---|
|
Int8Array %Int8Array% |
|
1 |
|
8-bit two's complement signed |
|
Uint8Array %Uint8Array% |
|
1 |
|
8-bit unsigned |
|
Uint8ClampedArray %Uint8ClampedArray% |
|
1 |
|
8-bit unsigned |
|
Int16Array %Int16Array% |
|
2 |
|
16-bit two's complement signed |
|
Uint16Array %Uint16Array% |
|
2 |
|
16-bit unsigned |
|
Int32Array %Int32Array% |
|
4 |
|
32-bit two's complement signed |
|
Uint32Array %Uint32Array% |
|
4 |
|
32-bit unsigned |
|
BigInt64Array %BigInt64Array% |
|
8 |
|
64-bit two's complement signed |
|
BigUint64Array %BigUint64Array% |
|
8 |
|
64-bit unsigned |
|
Float16Array %Float16Array% |
|
2 | 16-bit IEEE floating point | |
|
Float32Array %Float32Array% |
|
4 | 32-bit IEEE floating point | |
|
Float64Array %Float64Array% |
|
8 | 64-bit IEEE floating point |
In the definitions below, references to TypedArray should be replaced with the appropriate
23.2.1 The %TypedArray% Intrinsic Object
The %TypedArray% intrinsic object:
- is a
constructor function object that all of the TypedArrayconstructor objects inherit from. - along with its corresponding prototype object, provides common properties that are inherited
by all TypedArray
constructors and their instances. - does not have a global name or appear as a property of the
global object . - acts as the abstract superclass of the various TypedArray
constructors . - will throw an error when invoked, because it is an abstract class
constructor . The TypedArrayconstructors do not perform asupercall to it.
23.2.1.1 %TypedArray% ( )
This function performs the following steps when called:
- Throw a
TypeError exception.
The
23.2.2 Properties of the %TypedArray% Intrinsic Object
The
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"name" property whose value is"TypedArray" . - has the following properties:
23.2.2.1 %TypedArray%.from ( source [ , mapper [ , thisArg ] ] )
This method performs the following steps when called:
- Let C be the
this value. - If
IsConstructor (C) isfalse , throw aTypeError exception. - If mapper is
undefined , then- Let mapping be
false .
- Let mapping be
- Else,
- If
IsCallable (mapper) isfalse , throw aTypeError exception. - Let mapping be
true .
- If
- Let usingIterator be ?
GetMethod (source,%Symbol.iterator% ). - If usingIterator is not
undefined , then- Let values be ?
IteratorToList (?GetIteratorFromMethod (source, usingIterator)). - Let len be the number of elements in values.
- Let targetObj be ?
TypedArrayCreateFromConstructor (C, «𝔽 (len) »). - Let k be 0.
- Repeat, while k < len,
Assert : values is now an emptyList .- Return targetObj.
- Let values be ?
- NOTE: source is not an
iterable object , so assume it is already anarray-like object . - Let arrayLike be !
ToObject (source). - Let len be ?
LengthOfArrayLike (arrayLike). - Let targetObj be ?
TypedArrayCreateFromConstructor (C, «𝔽 (len) »). - Let k be 0.
- Repeat, while k < len,
- Return targetObj.
23.2.2.2 %TypedArray%.of ( ...items )
This method performs the following steps when called:
- Let len be the number of elements in items.
- Let C be the
this value. - If
IsConstructor (C) isfalse , throw aTypeError exception. - Let newObj be ?
TypedArrayCreateFromConstructor (C, «𝔽 (len) »). - Let k be 0.
- Repeat, while k < len,
- Return newObj.
23.2.2.3 %TypedArray%.prototype
The initial value of .prototype
is the
This property has the attributes { [[Writable]]:
23.2.2.4 get %TypedArray% [ %Symbol.species% ]
[%Symbol.species%]
is an
- Return the
this value.
The value of the
23.2.3 Properties of the %TypedArray% Prototype Object
The %TypedArray% prototype object:
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is %TypedArray.prototype%.
- is an
ordinary object . - does not have a [[ViewedArrayBuffer]] or any other of the internal slots that are specific to TypedArray instance objects.
23.2.3.1 %TypedArray%.prototype.at ( index )
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let relativeIndex be ?
ToIntegerOrInfinity (index). - If relativeIndex ≥ 0, then
- Let k be relativeIndex.
- Else,
- Let k be len + relativeIndex.
- If k < 0 or k ≥ len, return
undefined . - Return !
Get (O, !ToString (𝔽 (k))).
23.2.3.2 get %TypedArray%.prototype.buffer
.prototype.buffer
is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[TypedArrayName]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let buffer be O.[[ViewedArrayBuffer]].
- Return buffer.
23.2.3.3 get %TypedArray%.prototype.byteLength
.prototype.byteLength
is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[TypedArrayName]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let taRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - Let size be
TypedArrayByteLength (taRecord). - Return
𝔽 (size).
23.2.3.4 get %TypedArray%.prototype.byteOffset
.prototype.byteOffset
is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[TypedArrayName]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let taRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , return+0 𝔽. - Let offset be O.[[ByteOffset]].
- Return
𝔽 (offset).
23.2.3.5 %TypedArray%.prototype.constructor
The initial value of .prototype.constructor
is
23.2.3.6 %TypedArray%.prototype.copyWithin ( target, start [ , end ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.copyWithin as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let relativeTarget be ?
ToIntegerOrInfinity (target). - If relativeTarget = -∞, let targetIndex be 0.
- Else if relativeTarget < 0, let targetIndex be
max (len + relativeTarget, 0). - Else, let targetIndex be
min (relativeTarget, len). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let startIndex be 0.
- Else if relativeStart < 0, let startIndex be
max (len + relativeStart, 0). - Else, let startIndex be
min (relativeStart, len). - If end is
undefined , let relativeEnd be len; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let endIndex be 0.
- Else if relativeEnd < 0, let endIndex be
max (len + relativeEnd, 0). - Else, let endIndex be
min (relativeEnd, len). - Let count be
min (endIndex - startIndex, len - targetIndex). - If count > 0, then
- NOTE: The copying must be performed in a manner that preserves the bit-level encoding of the source data.
- Let buffer be O.[[ViewedArrayBuffer]].
- Set taRecord to
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Set len to
TypedArrayLength (taRecord). - Let elementSize be
TypedArrayElementSize (O). - Let byteOffset be O.[[ByteOffset]].
- Let bufferByteLimit be (len × elementSize) + byteOffset.
- Let toByteIndex be (targetIndex × elementSize) + byteOffset.
- Let fromByteIndex be (startIndex × elementSize) + byteOffset.
- Let countBytes be count × elementSize.
- If fromByteIndex < toByteIndex and
toByteIndex < fromByteIndex +
countBytes, then
- Let direction be -1.
- Set fromByteIndex to fromByteIndex + countBytes - 1.
- Set toByteIndex to toByteIndex + countBytes - 1.
- Else,
- Let direction be 1.
- Repeat, while countBytes > 0,
- If fromByteIndex < bufferByteLimit and
toByteIndex < bufferByteLimit, then
- Let value be
GetValueFromBuffer (buffer, fromByteIndex,uint8 ,true ,unordered ). - Perform
SetValueInBuffer (buffer, toByteIndex,uint8 , value,true ,unordered ). - Set fromByteIndex to fromByteIndex + direction.
- Set toByteIndex to toByteIndex + direction.
- Set countBytes to countBytes - 1.
- Let value be
- Else,
- Set countBytes to 0.
- If fromByteIndex < bufferByteLimit and
toByteIndex < bufferByteLimit, then
- Return O.
23.2.3.7 %TypedArray%.prototype.entries ( )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
ValidateTypedArray (O,seq-cst ). - Return
CreateArrayIterator (O,key+value ).
23.2.3.8 %TypedArray%.prototype.every ( callback [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.every as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If
IsCallable (callback) isfalse , throw aTypeError exception. - Let k be 0.
- Repeat, while k < len,
- Return
true .
This method is not generic. The
23.2.3.9 %TypedArray%.prototype.fill ( value [ , start [ , end ] ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.fill as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If O.[[ContentType]] is
bigint , set value to ?ToBigInt (value). - Otherwise, set value to ?
ToNumber (value). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let startIndex be 0.
- Else if relativeStart < 0, let startIndex be
max (len + relativeStart, 0). - Else, let startIndex be
min (relativeStart, len). - If end is
undefined , let relativeEnd be len; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let endIndex be 0.
- Else if relativeEnd < 0, let endIndex be
max (len + relativeEnd, 0). - Else, let endIndex be
min (relativeEnd, len). - Set taRecord to
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Set len to
TypedArrayLength (taRecord). - Set endIndex to
min (endIndex, len). - Let k be startIndex.
- Repeat, while k < endIndex,
- Return O.
23.2.3.10 %TypedArray%.prototype.filter ( callback [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.filter as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If
IsCallable (callback) isfalse , throw aTypeError exception. - Let kept be a new empty
List . - Let captured be 0.
- Let k be 0.
- Repeat, while k < len,
- Let A be ?
TypedArraySpeciesCreate (O, «𝔽 (captured) »). - Let n be 0.
- For each element e of kept, do
- Return A.
This method is not generic. The
23.2.3.11 %TypedArray%.prototype.find ( predicate [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.find as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let findRec be ?
FindViaPredicate (O, len,ascending , predicate, thisArg). - Return findRec.[[Value]].
This method is not generic. The
23.2.3.12 %TypedArray%.prototype.findIndex ( predicate [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.findIndex as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let findRec be ?
FindViaPredicate (O, len,ascending , predicate, thisArg). - Return findRec.[[Index]].
This method is not generic. The
23.2.3.13 %TypedArray%.prototype.findLast ( predicate [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.findLast as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let findRec be ?
FindViaPredicate (O, len,descending , predicate, thisArg). - Return findRec.[[Value]].
This method is not generic. The
23.2.3.14 %TypedArray%.prototype.findLastIndex ( predicate [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.findLastIndex as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let findRec be ?
FindViaPredicate (O, len,descending , predicate, thisArg). - Return findRec.[[Index]].
This method is not generic. The
23.2.3.15 %TypedArray%.prototype.forEach ( callback [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.forEach as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If
IsCallable (callback) isfalse , throw aTypeError exception. - Let k be 0.
- Repeat, while k < len,
- Return
undefined .
This method is not generic. The
23.2.3.16 %TypedArray%.prototype.includes ( searchElement [ , fromIndex ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.includes as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If len = 0, return
false . - Let n be ?
ToIntegerOrInfinity (fromIndex). Assert : If fromIndex isundefined , then n is 0.- If n = +∞, return
false . - Else if n = -∞, set n to 0.
- If n ≥ 0, then
- Let k be n.
- Else,
- Let k be len + n.
- If k < 0, set k to 0.
- Repeat, while k < len,
- Let elementK be !
Get (O, !ToString (𝔽 (k))). - If
SameValueZero (searchElement, elementK) istrue , returntrue . - Set k to k + 1.
- Let elementK be !
- Return
false .
This method is not generic. The
23.2.3.17 %TypedArray%.prototype.indexOf ( searchElement [ , fromIndex ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.indexOf as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If len = 0, return
-1 𝔽. - Let n be ?
ToIntegerOrInfinity (fromIndex). Assert : If fromIndex isundefined , then n is 0.- If n = +∞, return
-1 𝔽. - Else if n = -∞, set n to 0.
- If n ≥ 0, then
- Let k be n.
- Else,
- Let k be len + n.
- If k < 0, set k to 0.
- Repeat, while k < len,
- Let Pk be !
ToString (𝔽 (k)). - Let kPresent be !
HasProperty (O, Pk). - If kPresent is
true , then- Let elementK be !
Get (O, Pk). - If
IsStrictlyEqual (searchElement, elementK) istrue , return𝔽 (k).
- Let elementK be !
- Set k to k + 1.
- Let Pk be !
- Return
-1 𝔽.
This method is not generic. The
23.2.3.18 %TypedArray%.prototype.join ( separator )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.join as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If separator is
undefined , let sep be"," . - Else, let sep be ?
ToString (separator). - Let R be the empty String.
- Let k be 0.
- Repeat, while k < len,
- If k > 0, set R to the
string-concatenation of R and sep. - Let element be !
Get (O, !ToString (𝔽 (k))). - If element is not
undefined , then- Let S be !
ToString (element). - Set R to the
string-concatenation of R and S.
- Let S be !
- Set k to k + 1.
- If k > 0, set R to the
- Return R.
This method is not generic. The
23.2.3.19 %TypedArray%.prototype.keys ( )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
ValidateTypedArray (O,seq-cst ). - Return
CreateArrayIterator (O,key ).
23.2.3.20 %TypedArray%.prototype.lastIndexOf ( searchElement [ , fromIndex ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.lastIndexOf as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If len = 0, return
-1 𝔽. - If fromIndex is present, let n be ?
ToIntegerOrInfinity (fromIndex); else let n be len - 1. - If n = -∞, return
-1 𝔽. - If n ≥ 0, then
- Let k be
min (n, len - 1).
- Let k be
- Else,
- Let k be len + n.
- Repeat, while k ≥ 0,
- Let Pk be !
ToString (𝔽 (k)). - Let kPresent be !
HasProperty (O, Pk). - If kPresent is
true , then- Let elementK be !
Get (O, Pk). - If
IsStrictlyEqual (searchElement, elementK) istrue , return𝔽 (k).
- Let elementK be !
- Set k to k - 1.
- Let Pk be !
- Return
-1 𝔽.
This method is not generic. The
23.2.3.21 get %TypedArray%.prototype.length
.prototype.length
is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[TypedArrayName]]). Assert : O has [[ViewedArrayBuffer]] and [[ArrayLength]] internal slots.- Let taRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , return+0 𝔽. - Let length be
TypedArrayLength (taRecord). - Return
𝔽 (length).
This function is not generic. The
23.2.3.22 %TypedArray%.prototype.map ( callback [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.map as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If
IsCallable (callback) isfalse , throw aTypeError exception. - Let A be ?
TypedArraySpeciesCreate (O, «𝔽 (len) »). - Let k be 0.
- Repeat, while k < len,
- Return A.
This method is not generic. The
23.2.3.23 %TypedArray%.prototype.reduce ( callback [ , initialValue ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.reduce as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If
IsCallable (callback) isfalse , throw aTypeError exception. - If len = 0 and initialValue is not present, throw a
TypeError exception. - Let k be 0.
- Let accumulator be
undefined . - If initialValue is present, then
- Set accumulator to initialValue.
- Else,
- Repeat, while k < len,
- Return accumulator.
This method is not generic. The
23.2.3.24 %TypedArray%.prototype.reduceRight ( callback [ , initialValue ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.reduceRight as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If
IsCallable (callback) isfalse , throw aTypeError exception. - If len = 0 and initialValue is not present, throw a
TypeError exception. - Let k be len - 1.
- Let accumulator be
undefined . - If initialValue is present, then
- Set accumulator to initialValue.
- Else,
- Repeat, while k ≥ 0,
- Return accumulator.
This method is not generic. The
23.2.3.25 %TypedArray%.prototype.reverse ( )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.reverse as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let middle be
floor (len / 2). - Let lower be 0.
- Repeat, while lower ≠ middle,
- Return O.
This method is not generic. The
23.2.3.26 %TypedArray%.prototype.set ( source [ , offset ] )
This method sets multiple values in this TypedArray, reading the values from source. The details differ based upon the type of source. The optional offset value indicates the first element index in this TypedArray where values are written. If omitted, it is assumed to be 0.
It performs the following steps when called:
- Let target be the
this value. - Perform ?
RequireInternalSlot (target, [[TypedArrayName]]). Assert : target has a [[ViewedArrayBuffer]] internal slot.- Let targetOffset be ?
ToIntegerOrInfinity (offset). - If targetOffset < 0, throw a
RangeError exception. - If source
is an Object that has a [[TypedArrayName]] internal slot, then- Perform ?
SetTypedArrayFromTypedArray (target, targetOffset, source).
- Perform ?
- Else,
- Perform ?
SetTypedArrayFromArrayLike (target, targetOffset, source).
- Perform ?
- Return
undefined .
This method is not generic. The
23.2.3.26.1 SetTypedArrayFromArrayLike ( target, targetOffset, source )
The abstract operation SetTypedArrayFromArrayLike takes arguments target (a
- Let targetRecord be
MakeTypedArrayWithBufferWitnessRecord (target,seq-cst ). - If
IsTypedArrayOutOfBounds (targetRecord) istrue , throw aTypeError exception. - Let targetLength be
TypedArrayLength (targetRecord). - Let src be ?
ToObject (source). - Let srcLength be ?
LengthOfArrayLike (src). - If targetOffset = +∞, throw a
RangeError exception. - If srcLength + targetOffset > targetLength,
throw a
RangeError exception. - Let k be 0.
- Repeat, while k < srcLength,
- Let Pk be !
ToString (𝔽 (k)). - Let value be ?
Get (src, Pk). - Let targetIndex be
𝔽 (targetOffset + k). - Perform ?
TypedArraySetElement (target, targetIndex, value). - Set k to k + 1.
- Let Pk be !
- Return
unused .
23.2.3.26.2 SetTypedArrayFromTypedArray ( target, targetOffset, source )
The abstract operation SetTypedArrayFromTypedArray takes arguments target (a
- Let targetBuffer be target.[[ViewedArrayBuffer]].
- Let targetRecord be
MakeTypedArrayWithBufferWitnessRecord (target,seq-cst ). - If
IsTypedArrayOutOfBounds (targetRecord) istrue , throw aTypeError exception. - Let targetLength be
TypedArrayLength (targetRecord). - Let srcBuffer be source.[[ViewedArrayBuffer]].
- Let srcRecord be
MakeTypedArrayWithBufferWitnessRecord (source,seq-cst ). - If
IsTypedArrayOutOfBounds (srcRecord) istrue , throw aTypeError exception. - Let srcLength be
TypedArrayLength (srcRecord). - Let targetType be
TypedArrayElementType (target). - Let targetElementSize be
TypedArrayElementSize (target). - Let targetByteOffset be target.[[ByteOffset]].
- Let srcType be
TypedArrayElementType (source). - Let srcElementSize be
TypedArrayElementSize (source). - Let srcByteOffset be source.[[ByteOffset]].
- If targetOffset = +∞, throw a
RangeError exception. - If srcLength + targetOffset > targetLength,
throw a
RangeError exception. - If target.[[ContentType]] is not
source.[[ContentType]], throw a
TypeError exception. - If
IsSharedArrayBuffer (srcBuffer) istrue ,IsSharedArrayBuffer (targetBuffer) istrue , and srcBuffer.[[ArrayBufferData]] is targetBuffer.[[ArrayBufferData]], let sameSharedArrayBuffer betrue ; otherwise let sameSharedArrayBuffer befalse . - If
SameValue (srcBuffer, targetBuffer) istrue or sameSharedArrayBuffer istrue , then- Let srcByteLength be
TypedArrayByteLength (srcRecord). - Set srcBuffer to ?
CloneArrayBuffer (srcBuffer, srcByteOffset, srcByteLength). - Let srcByteIndex be 0.
- Let srcByteLength be
- Else,
- Let srcByteIndex be srcByteOffset.
- Let targetByteIndex be (targetOffset × targetElementSize) + targetByteOffset.
- Let limit be targetByteIndex + (targetElementSize × srcLength).
- If srcType is targetType, then
- NOTE: The transfer must be performed in a manner that preserves the bit-level encoding of the source data.
- Repeat, while targetByteIndex < limit,
- Let value be
GetValueFromBuffer (srcBuffer, srcByteIndex,uint8 ,true ,unordered ). - Perform
SetValueInBuffer (targetBuffer, targetByteIndex,uint8 , value,true ,unordered ). - Set srcByteIndex to srcByteIndex + 1.
- Set targetByteIndex to targetByteIndex + 1.
- Let value be
- Else,
- Repeat, while targetByteIndex < limit,
- Let value be
GetValueFromBuffer (srcBuffer, srcByteIndex, srcType,true ,unordered ). - Perform
SetValueInBuffer (targetBuffer, targetByteIndex, targetType, value,true ,unordered ). - Set srcByteIndex to srcByteIndex + srcElementSize.
- Set targetByteIndex to targetByteIndex + targetElementSize.
- Let value be
- Repeat, while targetByteIndex < limit,
- Return
unused .
23.2.3.27 %TypedArray%.prototype.slice ( start, end )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.slice as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let srcArrayLength be
TypedArrayLength (taRecord). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let startIndex be 0.
- Else if relativeStart < 0, let startIndex be
max (srcArrayLength + relativeStart, 0). - Else, let startIndex be
min (relativeStart, srcArrayLength). - If end is
undefined , let relativeEnd be srcArrayLength; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let endIndex be 0.
- Else if relativeEnd < 0, let endIndex be
max (srcArrayLength + relativeEnd, 0). - Else, let endIndex be
min (relativeEnd, srcArrayLength). - Let countBytes be
max (endIndex - startIndex, 0). - Let A be ?
TypedArraySpeciesCreate (O, «𝔽 (countBytes) »). - If countBytes > 0, then
- Set taRecord to
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Set endIndex to
min (endIndex,TypedArrayLength (taRecord)). - Set countBytes to
max (endIndex - startIndex, 0). - Let srcType be
TypedArrayElementType (O). - Let targetType be
TypedArrayElementType (A). - If srcType is targetType, then
- NOTE: The transfer must be performed in a manner that preserves the bit-level encoding of the source data.
- Let srcBuffer be O.[[ViewedArrayBuffer]].
- Let targetBuffer be A.[[ViewedArrayBuffer]].
- Let elementSize be
TypedArrayElementSize (O). - Let srcByteOffset be O.[[ByteOffset]].
- Let srcByteIndex be (startIndex × elementSize) + srcByteOffset.
- Let targetByteIndex be A.[[ByteOffset]].
- Let endByteIndex be targetByteIndex + (countBytes × elementSize).
- Repeat, while targetByteIndex <
endByteIndex,
- Let value be
GetValueFromBuffer (srcBuffer, srcByteIndex,uint8 ,true ,unordered ). - Perform
SetValueInBuffer (targetBuffer, targetByteIndex,uint8 , value,true ,unordered ). - Set srcByteIndex to srcByteIndex + 1.
- Set targetByteIndex to targetByteIndex + 1.
- Let value be
- Else,
- Set taRecord to
- Return A.
This method is not generic. The
23.2.3.28 %TypedArray%.prototype.some ( callback [ , thisArg ] )
The interpretation and use of the arguments of this method are the same as for
Array.prototype.some as defined in
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - If
IsCallable (callback) isfalse , throw aTypeError exception. - Let k be 0.
- Repeat, while k < len,
- Return
false .
This method is not generic. The
23.2.3.29 %TypedArray%.prototype.sort ( comparator )
This is a distinct method that, except as described below, implements the same requirements
as those of Array.prototype.sort as defined in
This method is not generic. The
It performs the following steps when called:
- If comparator is not
undefined andIsCallable (comparator) isfalse , throw aTypeError exception. - Let obj be the
this value. - Let taRecord be ?
ValidateTypedArray (obj,seq-cst ). - Let len be
TypedArrayLength (taRecord). - NOTE: The following closure performs a numeric comparison rather than the string
comparison used in
23.1.3.30 . - Let SortCompare be a new
Abstract Closure with parameters (x, y) that captures comparator and performs the following steps when called:- Return ?
CompareTypedArrayElements (x, y, comparator).
- Return ?
- Let sortedList be ?
SortIndexedProperties (obj, len, SortCompare,read-through-holes ). - Let j be 0.
- Repeat, while j < len,
- Return obj.
Because
23.2.3.30 %TypedArray%.prototype.subarray ( start, end )
This method returns a new TypedArray whose element type is the element type of
this TypedArray and whose ArrayBuffer is the ArrayBuffer of this
TypedArray, referencing the elements in the
It performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[TypedArrayName]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let buffer be O.[[ViewedArrayBuffer]].
- Let srcRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (srcRecord) istrue , then- Let srcLength be 0.
- Else,
- Let srcLength be
TypedArrayLength (srcRecord).
- Let srcLength be
- Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let startIndex be 0.
- Else if relativeStart < 0, let startIndex be
max (srcLength + relativeStart, 0). - Else, let startIndex be
min (relativeStart, srcLength). - Let elementSize be
TypedArrayElementSize (O). - Let srcByteOffset be O.[[ByteOffset]].
- Let beginByteOffset be srcByteOffset + (startIndex × elementSize).
- If O.[[ArrayLength]] is
auto and end isundefined , then- Let argumentsList be « buffer,
𝔽 (beginByteOffset) ».
- Let argumentsList be « buffer,
- Else,
- If end is
undefined , let relativeEnd be srcLength; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let endIndex be 0.
- Else if relativeEnd < 0, let endIndex be
max (srcLength + relativeEnd, 0). - Else, let endIndex be
min (relativeEnd, srcLength). - Let newLength be
max (endIndex - startIndex, 0). - Let argumentsList be « buffer,
𝔽 (beginByteOffset),𝔽 (newLength) ».
- If end is
- Return ?
TypedArraySpeciesCreate (O, argumentsList).
This method is not generic. The
23.2.3.31 %TypedArray%.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
This is a distinct method that implements the same algorithm as
Array.prototype.toLocaleString as defined in
This method is not generic.
If the ECMAScript implementation includes the ECMA-402 Internationalization API this
method is based upon the algorithm for Array.prototype.toLocaleString
that is in the ECMA-402 specification.
23.2.3.32 %TypedArray%.prototype.toReversed ( )
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let length be
TypedArrayLength (taRecord). - Let A be ?
TypedArrayCreateSameType (O, «𝔽 (length) »). - Let k be 0.
- Repeat, while k < length,
- Return A.
23.2.3.33 %TypedArray%.prototype.toSorted ( comparator )
This method performs the following steps when called:
- If comparator is not
undefined andIsCallable (comparator) isfalse , throw aTypeError exception. - Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let A be ?
TypedArrayCreateSameType (O, «𝔽 (len) »). - NOTE: The following closure performs a numeric comparison rather than the string
comparison used in
23.1.3.34 . - Let SortCompare be a new
Abstract Closure with parameters (x, y) that captures comparator and performs the following steps when called:- Return ?
CompareTypedArrayElements (x, y, comparator).
- Return ?
- Let sortedList be ?
SortIndexedProperties (O, len, SortCompare,read-through-holes ). - Let j be 0.
- Repeat, while j < len,
- Return A.
23.2.3.34 %TypedArray%.prototype.toString ( )
The initial value of the
23.2.3.35 %TypedArray%.prototype.values ( )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
ValidateTypedArray (O,seq-cst ). - Return
CreateArrayIterator (O,value ).
23.2.3.36 %TypedArray%.prototype.with ( index, value )
This method performs the following steps when called:
- Let O be the
this value. - Let taRecord be ?
ValidateTypedArray (O,seq-cst ). - Let len be
TypedArrayLength (taRecord). - Let relativeIndex be ?
ToIntegerOrInfinity (index). - If relativeIndex ≥ 0, let actualIndex be relativeIndex.
- Else, let actualIndex be len + relativeIndex.
- If O.[[ContentType]] is
bigint , let numericValue be ?ToBigInt (value). - Else, let numericValue be ?
ToNumber (value). - If
IsValidIntegerIndex (O,𝔽 (actualIndex)) isfalse , throw aRangeError exception. - Let A be ?
TypedArrayCreateSameType (O, «𝔽 (len) »). - Let k be 0.
- Repeat, while k < len,
- Return A.
23.2.3.37 %TypedArray%.prototype [ %Symbol.iterator% ] ( )
The initial value of the
23.2.3.38 get %TypedArray%.prototype [ %Symbol.toStringTag% ]
.prototype[%Symbol.toStringTag%]
is an
- Let O be the
this value. - If O
is not an Object , returnundefined . - If O does not have a [[TypedArrayName]] internal
slot, return
undefined . - Let name be O.[[TypedArrayName]].
Assert : nameis a String .- Return name.
This property has the attributes { [[Enumerable]]:
The initial value of the
23.2.4 Abstract Operations for TypedArray Objects
23.2.4.1 TypedArrayCreateFromConstructor ( constructor, argumentList )
The abstract operation TypedArrayCreateFromConstructor takes arguments constructor
(a
- Let newTypedArray be ?
Construct (constructor, argumentList). - Let taRecord be ?
ValidateTypedArray (newTypedArray,seq-cst ). Assert : newTypedArray has all the internal slots mentioned inProperties of TypedArray Instances .- If the number of elements in argumentList is 1 and
argumentList[0]
is a Number , then- If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Let length be
TypedArrayLength (taRecord). - If length <
ℝ (argumentList[0]), throw aTypeError exception.
- If
- Return newTypedArray.
23.2.4.2 TypedArrayCreateSameType ( exemplar, argumentList )
The abstract operation TypedArrayCreateSameType takes arguments exemplar (a
- Let constructor be the intrinsic object associated with the
constructor name exemplar.[[TypedArrayName]] inTable 75 . - Let result be ?
TypedArrayCreateFromConstructor (constructor, argumentList). Assert : result.[[ContentType]] is exemplar.[[ContentType]].- Return result.
23.2.4.3 TypedArraySpeciesCreate ( exemplar, argumentList )
The abstract operation TypedArraySpeciesCreate takes arguments exemplar (a
- Let defaultConstructor be the intrinsic object associated with the
constructor name exemplar.[[TypedArrayName]] inTable 75 . - Let constructor be ?
SpeciesConstructor (exemplar, defaultConstructor). - Let result be ?
TypedArrayCreateFromConstructor (constructor, argumentList). - If result.[[ContentType]] is not
exemplar.[[ContentType]], throw a
TypeError exception. - Return result.
23.2.4.4 ValidateTypedArray ( O, order )
The abstract operation ValidateTypedArray takes arguments O (an
- Perform ?
RequireInternalSlot (O, [[TypedArrayName]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let taRecord be
MakeTypedArrayWithBufferWitnessRecord (O, order). - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Return taRecord.
23.2.4.5 TypedArrayElementSize ( O )
The abstract operation TypedArrayElementSize takes argument O (a
- Return the Element Size value specified in
Table 75 for O.[[TypedArrayName]].
23.2.4.6 TypedArrayElementType ( O )
The abstract operation TypedArrayElementType takes argument O (a
- Return the Element Type value specified in
Table 75 for O.[[TypedArrayName]].
23.2.4.7 CompareTypedArrayElements ( x, y, comparator )
The abstract operation CompareTypedArrayElements takes arguments x (a Number or a
BigInt), y (a Number or a BigInt), and comparator (a
Assert : xis a Number and yis a Number , or xis a BigInt and yis a BigInt .- If comparator is not
undefined , then - If x and y are both
NaN , return+0 𝔽. - If x is
NaN , return1 𝔽. - If y is
NaN , return-1 𝔽. - If x < y, return
-1 𝔽. - If x > y, return
1 𝔽. - If x is
-0 𝔽 and y is+0 𝔽, return-1 𝔽. - If x is
+0 𝔽 and y is-0 𝔽, return1 𝔽. - Return
+0 𝔽.
23.2.5 The TypedArray Constructors
Each TypedArray
- is an intrinsic object that has the structure described below, differing only in the name
used as the
constructor name instead of TypedArray, inTable 75 . - is a function whose behaviour differs based upon the number and types of its arguments. The actual behaviour of a call of TypedArray depends upon the number and kind of arguments that are passed to it.
- is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified TypedArray behaviour must include asupercall to the TypedArrayconstructor to create and initialize the subclass instance with the internal state necessary to support the%TypedArray% .prototypebuilt-in methods.
23.2.5.1 TypedArray ( ...args )
Each TypedArray
- If NewTarget is
undefined , throw aTypeError exception. - Let constructorName be the String value of the
Constructor Name value specified inTable 75 for this TypedArrayconstructor . - Let proto be
"%TypedArray.prototype%". - Let numberOfArgs be the number of elements in args.
- If numberOfArgs = 0, then
- Return ?
AllocateTypedArray (constructorName, NewTarget, proto, 0).
- Return ?
- Else,
- Let firstArgument be args[0].
- If firstArgument
is an Object , then- Let O be ?
AllocateTypedArray (constructorName, NewTarget, proto). - If firstArgument has a [[TypedArrayName]] internal slot, then
- Perform ?
InitializeTypedArrayFromTypedArray (O, firstArgument).
- Perform ?
- Else if firstArgument has an [[ArrayBufferData]] internal slot, then
- If numberOfArgs > 1, let byteOffset
be args[1]; else let byteOffset be
undefined . - If numberOfArgs > 2, let length be
args[2]; else let length be
undefined . - Perform ?
InitializeTypedArrayFromArrayBuffer (O, firstArgument, byteOffset, length).
- If numberOfArgs > 1, let byteOffset
be args[1]; else let byteOffset be
- Else,
Assert : firstArgumentis an Object and firstArgument does not have either a [[TypedArrayName]] or an [[ArrayBufferData]] internal slot.- Let usingIterator be ?
GetMethod (firstArgument,%Symbol.iterator% ). - If usingIterator is not
undefined , then- Let values be ?
IteratorToList (?GetIteratorFromMethod (firstArgument, usingIterator)). - Perform ?
InitializeTypedArrayFromList (O, values).
- Let values be ?
- Else,
- NOTE: firstArgument is not an
iterable object , so assume it is already anarray-like object . - Perform ?
InitializeTypedArrayFromArrayLike (O, firstArgument).
- NOTE: firstArgument is not an
- Return O.
- Let O be ?
- Else,
Assert : firstArgumentis not an Object .- Let elementLength be ?
ToIndex (firstArgument). - Return ?
AllocateTypedArray (constructorName, NewTarget, proto, elementLength).
23.2.5.1.1 AllocateTypedArray ( constructorName, newTarget, defaultProto [ , length ] )
The abstract operation AllocateTypedArray takes arguments constructorName (a
String which is the name of a
- Let proto be ?
GetPrototypeFromConstructor (newTarget, defaultProto). - Let obj be
TypedArrayCreate (proto). Assert : obj.[[ViewedArrayBuffer]] isundefined .- Set obj.[[TypedArrayName]] to constructorName.
- If constructorName is either
"BigInt64Array" or"BigUint64Array" , set obj.[[ContentType]] tobigint . - Otherwise, set obj.[[ContentType]] to
number . - If length is not present, then
- Set obj.[[ByteLength]] to 0.
- Set obj.[[ByteOffset]] to 0.
- Set obj.[[ArrayLength]] to 0.
- Else,
- Perform ?
AllocateTypedArrayBuffer (obj, length).
- Perform ?
- Return obj.
23.2.5.1.2 InitializeTypedArrayFromTypedArray ( O, srcArray )
The abstract operation InitializeTypedArrayFromTypedArray takes arguments O (a
- Let srcData be srcArray.[[ViewedArrayBuffer]].
- Let elementType be
TypedArrayElementType (O). - Let elementSize be
TypedArrayElementSize (O). - Let srcType be
TypedArrayElementType (srcArray). - Let srcElementSize be
TypedArrayElementSize (srcArray). - Let srcByteOffset be srcArray.[[ByteOffset]].
- Let srcRecord be
MakeTypedArrayWithBufferWitnessRecord (srcArray,seq-cst ). - If
IsTypedArrayOutOfBounds (srcRecord) istrue , throw aTypeError exception. - Let elementLength be
TypedArrayLength (srcRecord). - Let byteLength be elementSize × elementLength.
- If elementType is srcType, then
- Let data be ?
CloneArrayBuffer (srcData, srcByteOffset, byteLength).
- Let data be ?
- Else,
- Let data be ?
AllocateArrayBuffer (%ArrayBuffer% , byteLength). - If srcArray.[[ContentType]] is not
O.[[ContentType]], throw a
TypeError exception. - Let srcByteIndex be srcByteOffset.
- Let targetByteIndex be 0.
- Let count be elementLength.
- Repeat, while count > 0,
- Let value be
GetValueFromBuffer (srcData, srcByteIndex, srcType,true ,unordered ). - Perform
SetValueInBuffer (data, targetByteIndex, elementType, value,true ,unordered ). - Set srcByteIndex to srcByteIndex + srcElementSize.
- Set targetByteIndex to targetByteIndex + elementSize.
- Set count to count - 1.
- Let value be
- Let data be ?
- Set O.[[ViewedArrayBuffer]] to data.
- Set O.[[ByteLength]] to byteLength.
- Set O.[[ByteOffset]] to 0.
- Set O.[[ArrayLength]] to elementLength.
- Return
unused .
23.2.5.1.3 InitializeTypedArrayFromArrayBuffer ( O, buffer, byteOffset, length )
The abstract operation InitializeTypedArrayFromArrayBuffer takes arguments O
(a
- Let elementSize be
TypedArrayElementSize (O). - Let offset be ?
ToIndex (byteOffset). - If offset
modulo elementSize ≠ 0, throw aRangeError exception. - Let bufferIsFixedLength be
IsFixedLengthArrayBuffer (buffer). - If length is not
undefined , then- Let newLength be ?
ToIndex (length).
- Let newLength be ?
- If
IsDetachedBuffer (buffer) istrue , throw aTypeError exception. - Let bufferByteLength be
ArrayBufferByteLength (buffer,seq-cst ). - If length is
undefined and bufferIsFixedLength isfalse , then- If offset > bufferByteLength, throw a
RangeError exception. - Set O.[[ByteLength]] to
auto . - Set O.[[ArrayLength]] to
auto .
- If offset > bufferByteLength, throw a
- Else,
- If length is
undefined , then- If bufferByteLength
modulo elementSize ≠ 0, throw aRangeError exception. - Let newByteLength be bufferByteLength - offset.
- If newByteLength < 0, throw a
RangeError exception.
- If bufferByteLength
- Else,
- Let newByteLength be newLength × elementSize.
- If offset + newByteLength >
bufferByteLength, throw a
RangeError exception.
- Set O.[[ByteLength]] to newByteLength.
- Set O.[[ArrayLength]] to newByteLength / elementSize.
- If length is
- Set O.[[ViewedArrayBuffer]] to buffer.
- Set O.[[ByteOffset]] to offset.
- Return
unused .
23.2.5.1.4 InitializeTypedArrayFromList ( O, values )
The abstract operation InitializeTypedArrayFromList takes arguments O (a
- Let len be the number of elements in values.
- Perform ?
AllocateTypedArrayBuffer (O, len). - Let k be 0.
- Repeat, while k < len,
Assert : values is now an emptyList .- Return
unused .
23.2.5.1.5 InitializeTypedArrayFromArrayLike ( O, arrayLike )
The abstract operation InitializeTypedArrayFromArrayLike takes arguments O (a
- Let len be ?
LengthOfArrayLike (arrayLike). - Perform ?
AllocateTypedArrayBuffer (O, len). - Let k be 0.
- Repeat, while k < len,
- Return
unused .
23.2.5.1.6 AllocateTypedArrayBuffer ( O, length )
The abstract operation AllocateTypedArrayBuffer takes arguments O (a
Assert : O.[[ViewedArrayBuffer]] isundefined .- Let elementSize be
TypedArrayElementSize (O). - Let byteLength be elementSize × length.
- Let data be ?
AllocateArrayBuffer (%ArrayBuffer% , byteLength). - Set O.[[ViewedArrayBuffer]] to data.
- Set O.[[ByteLength]] to byteLength.
- Set O.[[ByteOffset]] to 0.
- Set O.[[ArrayLength]] to length.
- Return
unused .
23.2.6 Properties of the TypedArray Constructors
Each TypedArray
- has a [[Prototype]] internal slot whose value is
%TypedArray% . - has a
"length" property whose value is3 𝔽. - has a
"name" property whose value is the String value of theconstructor name specified for it inTable 75 . - has the following properties:
23.2.6.1 TypedArray.BYTES_PER_ELEMENT
The value of TypedArray.BYTES_PER_ELEMENT is the Element Size value
specified in
This property has the attributes { [[Writable]]:
23.2.6.2 TypedArray.prototype
The initial value of TypedArray.prototype is the corresponding
TypedArray prototype intrinsic object (
This property has the attributes { [[Writable]]:
23.2.7 Properties of the TypedArray Prototype Objects
Each TypedArray prototype object:
- has a [[Prototype]] internal slot whose value is
%TypedArray.prototype% . - is an
ordinary object . - does not have a [[ViewedArrayBuffer]] or any other of the internal slots that are specific to TypedArray instance objects.
23.2.7.1 TypedArray.prototype.BYTES_PER_ELEMENT
The value of TypedArray.prototype.BYTES_PER_ELEMENT is the Element
Size value specified in
This property has the attributes { [[Writable]]:
23.2.7.2 TypedArray.prototype.constructor
The initial value of the
23.2.8 Properties of TypedArray Instances
TypedArray instances are
24 Keyed Collections
24.1 Map Objects
Maps are collections of key/value pairs where both the keys and values may be arbitrary
Maps must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of elements in the collection. The data structure used in this specification is only intended to describe the required observable semantics of Maps. It is not intended to be a viable implementation model.
24.1.1 The Map Constructor
The Map
- is %Map%.
- is the initial value of the
"Map" property of theglobal object . - creates and initializes a new Map when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Map behaviour must include asupercall to the Mapconstructor to create and initialize the subclass instance with the internal state necessary to support theMap.prototypebuilt-in methods.
24.1.1.1 Map ( [ iterable ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Let map be ?
OrdinaryCreateFromConstructor (NewTarget,"%Map.prototype%" , « [[MapData]] »). - Set map.[[MapData]] to a new empty
List . - If iterable is either
undefined ornull , return map. - Let adder be ?
Get (map,"set" ). - If
IsCallable (adder) isfalse , throw aTypeError exception. - Return ?
AddEntriesFromIterable (map, iterable, adder).
If the parameter iterable is present, it is expected to be an object that
implements a
24.1.1.2 AddEntriesFromIterable ( target, iterable, adder )
The abstract operation AddEntriesFromIterable takes arguments target (an Object),
iterable (an
- Let iteratorRecord be ?
GetIterator (iterable,sync ). - Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , return target. - If next
is not an Object , then- Let error be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iteratorRecord, error).
- Let error be
- Let k be
Completion (Get (next,"0" )). IfAbruptCloseIterator (k, iteratorRecord).- Let v be
Completion (Get (next,"1" )). IfAbruptCloseIterator (v, iteratorRecord).- Let status be
Completion (Call (adder, target, « k, v »)). IfAbruptCloseIterator (status, iteratorRecord).
- Let next be ?
The parameter iterable is expected to be an object that implements a
24.1.2 Properties of the Map Constructor
The Map
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
24.1.2.1 Map.groupBy ( items, callback )
callback should be a function that accepts two arguments.
groupBy calls callback once for each element in
items, in ascending order, and constructs a new Map. Each value returned
by callback is used as a key in the Map. For each such key, the result
Map has an entry whose key is that key and whose value is an array containing all
the elements for which callback returned that key.
callback is called with two arguments: the value of the element and the index of the element.
The return value of groupBy is a Map.
This function performs the following steps when called:
- Let groups be ?
GroupBy (items, callback,collection ). - Let map be !
Construct (%Map% ). - For each
Record { [[Key]], [[Elements]] } g of groups, do- Let elements be
CreateArrayFromList (g.[[Elements]]). - Let entry be the
Record { [[Key]]: g.[[Key]], [[Value]]: elements }. - Append entry to map.[[MapData]].
- Let elements be
- Return map.
24.1.2.2 Map.prototype
The initial value of Map.prototype is the
This property has the attributes { [[Writable]]:
24.1.2.3 get Map [ %Symbol.species% ]
Map[%Symbol.species%] is an
- Return the
this value.
The value of the
Methods that create derived collection objects should call
24.1.3 Properties of the Map Prototype Object
The Map prototype object:
- is %Map.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a [[MapData]] internal slot.
24.1.3.1 Map.prototype.clear ( )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[MapData]]). - For each
Record { [[Key]], [[Value]] } p of M.[[MapData]], do- Set p.[[Key]] to
empty . - Set p.[[Value]] to
empty .
- Set p.[[Key]] to
- Return
undefined .
The existing [[MapData]]
24.1.3.2 Map.prototype.constructor
The initial value of Map.prototype.constructor is
24.1.3.3 Map.prototype.delete ( key )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[MapData]]). - Set key to
CanonicalizeKeyedCollectionKey (key). - For each
Record { [[Key]], [[Value]] } p of M.[[MapData]], do- If p.[[Key]] is not
empty andSameValue (p.[[Key]], key) istrue , then- Set p.[[Key]] to
empty . - Set p.[[Value]] to
empty . - Return
true .
- Set p.[[Key]] to
- If p.[[Key]] is not
- Return
false .
The value
24.1.3.4 Map.prototype.entries ( )
This method performs the following steps when called:
- Let M be the
this value. - Return ?
CreateMapIterator (M,key+value ).
24.1.3.5 Map.prototype.forEach ( callback [ , thisArg ] )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[MapData]]). - If
IsCallable (callback) isfalse , throw aTypeError exception. - Let entries be M.[[MapData]].
- Let numEntries be the number of elements in entries.
- Let index be 0.
- Repeat, while index < numEntries,
- Let e be entries[index].
- Set index to index + 1.
- If e.[[Key]] is not
empty , then- Perform ?
Call (callback, thisArg, « e.[[Value]], e.[[Key]], M »). - NOTE: The number of elements in entries may have increased during execution of callback.
- Set numEntries to the number of elements in entries.
- Perform ?
- Return
undefined .
callback should be a function that accepts three arguments.
forEach calls callback once for each key/value pair present
in the Map, in key insertion order. callback is called only for keys of
the Map which actually exist; it is not called for keys that have been deleted from
the Map.
If a thisArg parameter is provided, it will be used as the
callback is called with three arguments: the value of the item, the key of the item, and the Map being traversed.
forEach does not directly mutate the object on which it is called but
the object may be mutated by the calls to callback. Each entry of a map's
[[MapData]] is only visited once. New keys added after the
call to forEach begins are visited. A key will be revisited if it is
deleted after it has been visited and then re-added before the forEach
call completes. Keys that are deleted after the call to forEach begins
and before being visited are not visited unless the key is added again before the
forEach call completes.
24.1.3.6 Map.prototype.get ( key )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[MapData]]). - Set key to
CanonicalizeKeyedCollectionKey (key). - For each
Record { [[Key]], [[Value]] } p of M.[[MapData]], do- If p.[[Key]] is not
empty andSameValue (p.[[Key]], key) istrue , return p.[[Value]].
- If p.[[Key]] is not
- Return
undefined .
24.1.3.7 Map.prototype.has ( key )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[MapData]]). - Set key to
CanonicalizeKeyedCollectionKey (key). - For each
Record { [[Key]], [[Value]] } p of M.[[MapData]], do- If p.[[Key]] is not
empty andSameValue (p.[[Key]], key) istrue , returntrue .
- If p.[[Key]] is not
- Return
false .
24.1.3.8 Map.prototype.keys ( )
This method performs the following steps when called:
- Let M be the
this value. - Return ?
CreateMapIterator (M,key ).
24.1.3.9 Map.prototype.set ( key, value )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[MapData]]). - Set key to
CanonicalizeKeyedCollectionKey (key). - For each
Record { [[Key]], [[Value]] } p of M.[[MapData]], do- If p.[[Key]] is not
empty andSameValue (p.[[Key]], key) istrue , then- Set p.[[Value]] to value.
- Return M.
- If p.[[Key]] is not
- Let p be the
Record { [[Key]]: key, [[Value]]: value }. - Append p to M.[[MapData]].
- Return M.
24.1.3.10 get Map.prototype.size
Map.prototype.size is an
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[MapData]]). - Let count be 0.
- For each
Record { [[Key]], [[Value]] } p of M.[[MapData]], do- If p.[[Key]] is not
empty , set count to count + 1.
- If p.[[Key]] is not
- Return
𝔽 (count).
24.1.3.11 Map.prototype.values ( )
This method performs the following steps when called:
- Let M be the
this value. - Return ?
CreateMapIterator (M,value ).
24.1.3.12 Map.prototype [ %Symbol.iterator% ] ( )
The initial value of the
24.1.3.13 Map.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
24.1.4 Properties of Map Instances
Map instances are
24.1.5 Map Iterator Objects
A Map
Iterator is an object that represents a specific iteration over some specific Map
instance object. There is not a named
24.1.5.1 CreateMapIterator ( map, kind )
The abstract operation CreateMapIterator takes arguments map (an
- Perform ?
RequireInternalSlot (map, [[MapData]]). - Let closure be a new
Abstract Closure with no parameters that captures map and kind and performs the following steps when called:- Let entries be map.[[MapData]].
- Let index be 0.
- Let numEntries be the number of elements in entries.
- Repeat, while index < numEntries,
- Let e be entries[index].
- Set index to index + 1.
- If e.[[Key]] is not
empty , then- If kind is
key , then- Let result be e.[[Key]].
- Else if kind is
value , then- Let result be e.[[Value]].
- Else,
Assert : kind iskey+value .- Let result be
CreateArrayFromList (« e.[[Key]], e.[[Value]] »).
- Perform ?
GeneratorYield (CreateIteratorResultObject (result,false )). - NOTE: The number of elements in entries may have
increased while execution of this abstract operation was
paused by
GeneratorYield . - Set numEntries to the number of elements in entries.
- If kind is
- Return
NormalCompletion (unused ).
- Return
CreateIteratorFromClosure (closure,"%MapIteratorPrototype%" ,%MapIteratorPrototype% ).
24.1.5.2 The %MapIteratorPrototype% Object
The %MapIteratorPrototype% object:
- has properties that are inherited by all
Map Iterator objects . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Iterator.prototype% . - has the following properties:
24.1.5.2.1 %MapIteratorPrototype%.next ( )
- Return ?
GeneratorResume (this value,empty ,"%MapIteratorPrototype%" ).
24.1.5.2.2 %MapIteratorPrototype% [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
24.2 Set Objects
Set objects are collections of
Set objects must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of elements in the collection. The data structure used in this specification is only intended to describe the required observable semantics of Set objects. It is not intended to be a viable implementation model.
24.2.1 Abstract Operations For Set Objects
24.2.1.1 Set Records
A Set Record is a
Set Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[SetObject]] | an Object | the Set or similar object. |
| [[Size]] |
a non-negative |
The reported size of the object. |
| [[Has]] |
a |
The has method of the object.
|
| [[Keys]] |
a |
The keys method of the object.
|
24.2.1.2 GetSetRecord ( obj )
The abstract operation GetSetRecord takes argument obj (an
- If obj
is not an Object , throw aTypeError exception. - Let rawSize be ?
Get (obj,"size" ). - Let numSize be ?
ToNumber (rawSize). - NOTE: If rawSize is
undefined , then numSize will beNaN . - If numSize is
NaN , throw aTypeError exception. - Let intSize be !
ToIntegerOrInfinity (numSize). - If intSize < 0, throw a
RangeError exception. - Let has be ?
Get (obj,"has" ). - If
IsCallable (has) isfalse , throw aTypeError exception. - Let keys be ?
Get (obj,"keys" ). - If
IsCallable (keys) isfalse , throw aTypeError exception. - Return a new
Set Record { [[SetObject]]: obj, [[Size]]: intSize, [[Has]]: has, [[Keys]]: keys }.
24.2.1.3 SetDataHas ( setData, value )
The abstract operation SetDataHas takes arguments setData (a
- If
SetDataIndex (setData, value) isnot-found , returnfalse . - Return
true .
24.2.1.4 SetDataIndex ( setData, value )
The abstract operation SetDataIndex takes arguments setData (a
- Set value to
CanonicalizeKeyedCollectionKey (value). - Let size be the number of elements in setData.
- Let index be 0.
- Repeat, while index < size,
- Let e be setData[index].
- If e is not
empty and e is value, then- Return index.
- Set index to index + 1.
- Return
not-found .
24.2.1.5 SetDataSize ( setData )
The abstract operation SetDataSize takes argument setData (a
- Let count be 0.
- For each element e of setData, do
- If e is not
empty , set count to count + 1.
- If e is not
- Return count.
24.2.2 The Set Constructor
The Set
- is %Set%.
- is the initial value of the
"Set" property of theglobal object . - creates and initializes a new Set object when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Set behaviour must include asupercall to the Setconstructor to create and initialize the subclass instance with the internal state necessary to support theSet.prototypebuilt-in methods.
24.2.2.1 Set ( [ iterable ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Let set be ?
OrdinaryCreateFromConstructor (NewTarget,"%Set.prototype%" , « [[SetData]] »). - Set set.[[SetData]] to a new empty
List . - If iterable is either
undefined ornull , return set. - Let adder be ?
Get (set,"add" ). - If
IsCallable (adder) isfalse , throw aTypeError exception. - Let iteratorRecord be ?
GetIterator (iterable,sync ). - Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , return set. - Let status be
Completion (Call (adder, set, « next »)). IfAbruptCloseIterator (status, iteratorRecord).
- Let next be ?
24.2.3 Properties of the Set Constructor
The Set
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
24.2.3.1 Set.prototype
The initial value of Set.prototype is the
This property has the attributes { [[Writable]]:
24.2.3.2 get Set [ %Symbol.species% ]
Set[%Symbol.species%] is an
- Return the
this value.
The value of the
Methods that create derived collection objects should call
24.2.4 Properties of the Set Prototype Object
The Set prototype object:
- is %Set.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a [[SetData]] internal slot.
24.2.4.1 Set.prototype.add ( value )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[SetData]]). - Set value to
CanonicalizeKeyedCollectionKey (value). - For each element e of S.[[SetData]],
do
- If e is not
empty andSameValue (e, value) istrue , then- Return S.
- If e is not
- Append value to S.[[SetData]].
- Return S.
24.2.4.2 Set.prototype.clear ( )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[SetData]]). - For each element e of S.[[SetData]],
do
- Replace the element of S.[[SetData]]
whose value is e with an element whose value is
empty .
- Replace the element of S.[[SetData]]
whose value is e with an element whose value is
- Return
undefined .
The existing [[SetData]]
24.2.4.3 Set.prototype.constructor
The initial value of Set.prototype.constructor is
24.2.4.4 Set.prototype.delete ( value )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[SetData]]). - Set value to
CanonicalizeKeyedCollectionKey (value). - For each element e of S.[[SetData]],
do
- If e is not
empty andSameValue (e, value) istrue , then- Replace the element of S.[[SetData]] whose value is e with
an element whose value is
empty . - Return
true .
- Replace the element of S.[[SetData]] whose value is e with
an element whose value is
- If e is not
- Return
false .
The value
24.2.4.5 Set.prototype.difference ( other )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[SetData]]). - Let otherRec be ?
GetSetRecord (other). - Let resultSetData be a copy of O.[[SetData]].
- If
SetDataSize (O.[[SetData]]) ≤ otherRec.[[Size]], then- Let thisSize be the number of elements in O.[[SetData]].
- Let index be 0.
- Repeat, while index < thisSize,
- Else,
- Let keysIter be ?
GetIteratorFromMethod (otherRec.[[SetObject]], otherRec.[[Keys]]). - Let next be
not-started . - Repeat, while next is not
done ,- Set next to ?
IteratorStepValue (keysIter). - If next is not
done , then- Set next to
CanonicalizeKeyedCollectionKey (next). - Let valueIndex be
SetDataIndex (resultSetData, next). - If valueIndex is not
not-found , then- Set resultSetData[valueIndex]
to
empty .
- Set resultSetData[valueIndex]
to
- Set next to
- Set next to ?
- Let keysIter be ?
- Let result be
OrdinaryObjectCreate (%Set.prototype% , « [[SetData]] »). - Set result.[[SetData]] to resultSetData.
- Return result.
24.2.4.6 Set.prototype.entries ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateSetIterator (S,key+value ).
For iteration purposes, a Set appears similar to a Map where each entry has the same value for its key and value.
24.2.4.7 Set.prototype.forEach ( callback [ , thisArg ] )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[SetData]]). - If
IsCallable (callback) isfalse , throw aTypeError exception. - Let entries be S.[[SetData]].
- Let numEntries be the number of elements in entries.
- Let index be 0.
- Repeat, while index < numEntries,
- Let e be entries[index].
- Set index to index + 1.
- If e is not
empty , then- Perform ?
Call (callback, thisArg, « e, e, S »). - NOTE: The number of elements in entries may have increased during execution of callback.
- Set numEntries to the number of elements in entries.
- Perform ?
- Return
undefined .
callback should be a function that accepts three arguments.
forEach calls callback once for each value present in the
Set object, in value insertion order. callback is called only for values
of the Set which actually exist; it is not called for keys that have been deleted
from the set.
If a thisArg parameter is provided, it will be used as the
callback is called with three arguments: the first two arguments are a value contained in the Set. The same value is passed for both arguments. The Set object being traversed is passed as the third argument.
The callback is called with three arguments to be consistent with the call
back functions used by forEach methods for Map and Array. For Sets,
each item value is considered to be both the key and the value.
forEach does not directly mutate the object on which it is called but
the object may be mutated by the calls to callback.
Each value is normally visited only once. However, a value will be revisited if it is
deleted after it has been visited and then re-added before the forEach
call completes. Values that are deleted after the call to forEach
begins and before being visited are not visited unless the value is added again
before the forEach call completes. New values added after the call to
forEach begins are visited.
24.2.4.8 Set.prototype.has ( value )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[SetData]]). - Set value to
CanonicalizeKeyedCollectionKey (value). - For each element e of S.[[SetData]],
do
- If e is not
empty andSameValue (e, value) istrue , returntrue .
- If e is not
- Return
false .
24.2.4.9 Set.prototype.intersection ( other )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[SetData]]). - Let otherRec be ?
GetSetRecord (other). - Let resultSetData be a new empty
List . - If
SetDataSize (O.[[SetData]]) ≤ otherRec.[[Size]], then- Let thisSize be the number of elements in O.[[SetData]].
- Let index be 0.
- Repeat, while index < thisSize,
- Let e be O.[[SetData]][index].
- Set index to index + 1.
- If e is not
empty , then- Let inOther be
ToBoolean (?Call (otherRec.[[Has]], otherRec.[[SetObject]], « e »)). - If inOther is
true , then- NOTE: It is possible for earlier calls to otherRec.[[Has]] to remove and re-add an element of O.[[SetData]], which can cause the same element to be visited twice during this iteration.
- If
SetDataHas (resultSetData, e) isfalse , then- Append e to resultSetData.
- NOTE: The number of elements in O.[[SetData]] may have increased during execution of otherRec.[[Has]].
- Set thisSize to the number of elements in O.[[SetData]].
- Let inOther be
- Else,
- Let keysIter be ?
GetIteratorFromMethod (otherRec.[[SetObject]], otherRec.[[Keys]]). - Let next be
not-started . - Repeat, while next is not
done ,- Set next to ?
IteratorStepValue (keysIter). - If next is not
done , then- Set next to
CanonicalizeKeyedCollectionKey (next). - Let inThis be
SetDataHas (O.[[SetData]], next). - If inThis is
true , then- NOTE: Because other is an arbitrary
object, it is possible for its
"keys" iterator to produce the same value more than once. - If
SetDataHas (resultSetData, next) isfalse , then- Append next to resultSetData.
- NOTE: Because other is an arbitrary
object, it is possible for its
- Set next to
- Set next to ?
- Let keysIter be ?
- Let result be
OrdinaryObjectCreate (%Set.prototype% , « [[SetData]] »). - Set result.[[SetData]] to resultSetData.
- Return result.
24.2.4.10 Set.prototype.isDisjointFrom ( other )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[SetData]]). - Let otherRec be ?
GetSetRecord (other). - If
SetDataSize (O.[[SetData]]) ≤ otherRec.[[Size]], then- Let thisSize be the number of elements in O.[[SetData]].
- Let index be 0.
- Repeat, while index < thisSize,
- Let e be O.[[SetData]][index].
- Set index to index + 1.
- If e is not
empty , then
- Else,
- Let keysIter be ?
GetIteratorFromMethod (otherRec.[[SetObject]], otherRec.[[Keys]]). - Let next be
not-started . - Repeat, while next is not
done ,- Set next to ?
IteratorStepValue (keysIter). - If next is not
done , then- If
SetDataHas (O.[[SetData]], next) istrue , then- Perform ?
IteratorClose (keysIter,NormalCompletion (unused )). - Return
false .
- Perform ?
- If
- Set next to ?
- Let keysIter be ?
- Return
true .
24.2.4.11 Set.prototype.isSubsetOf ( other )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[SetData]]). - Let otherRec be ?
GetSetRecord (other). - If
SetDataSize (O.[[SetData]]) > otherRec.[[Size]], returnfalse . - Let thisSize be the number of elements in O.[[SetData]].
- Let index be 0.
- Repeat, while index < thisSize,
- Let e be O.[[SetData]][index].
- Set index to index + 1.
- If e is not
empty , then
- Return
true .
24.2.4.12 Set.prototype.isSupersetOf ( other )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[SetData]]). - Let otherRec be ?
GetSetRecord (other). - If
SetDataSize (O.[[SetData]]) < otherRec.[[Size]], returnfalse . - Let keysIter be ?
GetIteratorFromMethod (otherRec.[[SetObject]], otherRec.[[Keys]]). - Let next be
not-started . - Repeat, while next is not
done ,- Set next to ?
IteratorStepValue (keysIter). - If next is not
done , then- If
SetDataHas (O.[[SetData]], next) isfalse , then- Perform ?
IteratorClose (keysIter,NormalCompletion (unused )). - Return
false .
- Perform ?
- If
- Set next to ?
- Return
true .
24.2.4.13 Set.prototype.keys ( )
The initial value of the
For iteration purposes, a Set appears similar to a Map where each entry has the same value for its key and value.
24.2.4.14 get Set.prototype.size
Set.prototype.size is an
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[SetData]]). - Let size be
SetDataSize (S.[[SetData]]). - Return
𝔽 (size).
24.2.4.15 Set.prototype.symmetricDifference ( other )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[SetData]]). - Let otherRec be ?
GetSetRecord (other). - Let keysIter be ?
GetIteratorFromMethod (otherRec.[[SetObject]], otherRec.[[Keys]]). - Let resultSetData be a copy of O.[[SetData]].
- Let next be
not-started . - Repeat, while next is not
done ,- Set next to ?
IteratorStepValue (keysIter). - If next is not
done , then- Set next to
CanonicalizeKeyedCollectionKey (next). - Let resultIndex be
SetDataIndex (resultSetData, next). - If resultIndex is
not-found , let alreadyInResult befalse ; otherwise let alreadyInResult betrue . - If
SetDataHas (O.[[SetData]], next) istrue , then- If alreadyInResult is
true , set resultSetData[resultIndex] toempty .
- If alreadyInResult is
- Else,
- If alreadyInResult is
false , append next to resultSetData.
- If alreadyInResult is
- Set next to
- Set next to ?
- Let result be
OrdinaryObjectCreate (%Set.prototype% , « [[SetData]] »). - Set result.[[SetData]] to resultSetData.
- Return result.
24.2.4.16 Set.prototype.union ( other )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[SetData]]). - Let otherRec be ?
GetSetRecord (other). - Let keysIter be ?
GetIteratorFromMethod (otherRec.[[SetObject]], otherRec.[[Keys]]). - Let resultSetData be a copy of O.[[SetData]].
- Let next be
not-started . - Repeat, while next is not
done ,- Set next to ?
IteratorStepValue (keysIter). - If next is not
done , then- Set next to
CanonicalizeKeyedCollectionKey (next). - If
SetDataHas (resultSetData, next) isfalse , then- Append next to resultSetData.
- Set next to
- Set next to ?
- Let result be
OrdinaryObjectCreate (%Set.prototype% , « [[SetData]] »). - Set result.[[SetData]] to resultSetData.
- Return result.
24.2.4.17 Set.prototype.values ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateSetIterator (S,value ).
24.2.4.18 Set.prototype [ %Symbol.iterator% ] ( )
The initial value of the
24.2.4.19 Set.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
24.2.5 Properties of Set Instances
Set instances are
24.2.6 Set Iterator Objects
A Set
Iterator is an
24.2.6.1 CreateSetIterator ( set, kind )
The abstract operation CreateSetIterator takes arguments set (an
- Perform ?
RequireInternalSlot (set, [[SetData]]). - Let closure be a new
Abstract Closure with no parameters that captures set and kind and performs the following steps when called:- Let index be 0.
- Let entries be set.[[SetData]].
- Let numEntries be the number of elements in entries.
- Repeat, while index < numEntries,
- Let e be entries[index].
- Set index to index + 1.
- If e is not
empty , then- If kind is
key+value , then- Let result be
CreateArrayFromList (« e, e »). - Perform ?
GeneratorYield (CreateIteratorResultObject (result,false )).
- Let result be
- Else,
Assert : kind isvalue .- Perform ?
GeneratorYield (CreateIteratorResultObject (e,false )).
- NOTE: The number of elements in entries may have
increased while execution of this abstract operation was
paused by
GeneratorYield . - Set numEntries to the number of elements in entries.
- If kind is
- Return
NormalCompletion (unused ).
- Return
CreateIteratorFromClosure (closure,"%SetIteratorPrototype%" ,%SetIteratorPrototype% ).
24.2.6.2 The %SetIteratorPrototype% Object
The %SetIteratorPrototype% object:
- has properties that are inherited by all
Set Iterator objects . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Iterator.prototype% . - has the following properties:
24.2.6.2.1 %SetIteratorPrototype%.next ( )
- Return ?
GeneratorResume (this value,empty ,"%SetIteratorPrototype%" ).
24.2.6.2.2 %SetIteratorPrototype% [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
24.3 WeakMap Objects
WeakMaps are collections of key/value pairs where the keys are objects and/or symbols and values may
be arbitrary
An implementation may impose an arbitrarily determined latency between the time a key/value pair of a WeakMap becomes inaccessible and the time when the key/value pair is removed from the WeakMap. If this latency was observable to ECMAScript program, it would be a source of indeterminacy that could impact program execution. For that reason, an ECMAScript implementation must not provide any means to observe a key of a WeakMap that does not require the observer to present the observed key.
WeakMaps must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of key/value pairs in the collection. The data structure used in this specification is only intended to describe the required observable semantics of WeakMaps. It is not intended to be a viable implementation model.
WeakMap and WeakSet are intended to provide mechanisms for dynamically associating state with an object or symbol in a manner that does not “leak” memory resources if, in the absence of the WeakMap or WeakSet instance, the object or symbol otherwise became inaccessible and subject to resource reclamation by the implementation's garbage collection mechanisms. This characteristic can be achieved by using an inverted per-object/symbol mapping of WeakMap or WeakSet instances to keys. Alternatively, each WeakMap or WeakSet instance may internally store its key and value data, but this approach requires coordination between the WeakMap or WeakSet implementation and the garbage collector. The following references describe mechanism that may be useful to implementations of WeakMap and WeakSet:
Barry Hayes. 1997. Ephemerons: a new finalization mechanism. In Proceedings of the 12th ACM SIGPLAN conference on Object-oriented programming, systems, languages, and applications (OOPSLA '97), A. Michael Berman (Ed.). ACM, New York, NY, USA, 176-183, http://doi.acm.org/10.1145/263698.263733.
Alexandra Barros, Roberto Ierusalimschy, Eliminating Cycles in Weak Tables. Journal of Universal Computer Science - J.UCS, vol. 14, no. 21, pp. 3481-3497, 2008, http://www.jucs.org/jucs_14_21/eliminating_cycles_in_weak
24.3.1 The WeakMap Constructor
The WeakMap
- is %WeakMap%.
- is the initial value of the
"WeakMap" property of theglobal object . - creates and initializes a new WeakMap when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified WeakMap behaviour must include asupercall to the WeakMapconstructor to create and initialize the subclass instance with the internal state necessary to support theWeakMap.prototypebuilt-in methods.
24.3.1.1 WeakMap ( [ iterable ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Let map be ?
OrdinaryCreateFromConstructor (NewTarget,"%WeakMap.prototype%" , « [[WeakMapData]] »). - Set map.[[WeakMapData]] to a new empty
List . - If iterable is either
undefined ornull , return map. - Let adder be ?
Get (map,"set" ). - If
IsCallable (adder) isfalse , throw aTypeError exception. - Return ?
AddEntriesFromIterable (map, iterable, adder).
If the parameter iterable is present, it is expected to be an object that
implements a
24.3.2 Properties of the WeakMap Constructor
The WeakMap
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
24.3.2.1 WeakMap.prototype
The initial value of WeakMap.prototype is the
This property has the attributes { [[Writable]]:
24.3.3 Properties of the WeakMap Prototype Object
The WeakMap prototype object:
- is %WeakMap.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a [[WeakMapData]] internal slot.
24.3.3.1 WeakMap.prototype.constructor
The initial value of WeakMap.prototype.constructor is
24.3.3.2 WeakMap.prototype.delete ( key )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[WeakMapData]]). - If
CanBeHeldWeakly (key) isfalse , returnfalse . - For each
Record { [[Key]], [[Value]] } p of M.[[WeakMapData]], do- If p.[[Key]] is not
empty andSameValue (p.[[Key]], key) istrue , then- Set p.[[Key]] to
empty . - Set p.[[Value]] to
empty . - Return
true .
- Set p.[[Key]] to
- If p.[[Key]] is not
- Return
false .
The value
24.3.3.3 WeakMap.prototype.get ( key )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[WeakMapData]]). - If
CanBeHeldWeakly (key) isfalse , returnundefined . - For each
Record { [[Key]], [[Value]] } p of M.[[WeakMapData]], do- If p.[[Key]] is not
empty andSameValue (p.[[Key]], key) istrue , return p.[[Value]].
- If p.[[Key]] is not
- Return
undefined .
24.3.3.4 WeakMap.prototype.has ( key )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[WeakMapData]]). - If
CanBeHeldWeakly (key) isfalse , returnfalse . - For each
Record { [[Key]], [[Value]] } p of M.[[WeakMapData]], do- If p.[[Key]] is not
empty andSameValue (p.[[Key]], key) istrue , returntrue .
- If p.[[Key]] is not
- Return
false .
24.3.3.5 WeakMap.prototype.set ( key, value )
This method performs the following steps when called:
- Let M be the
this value. - Perform ?
RequireInternalSlot (M, [[WeakMapData]]). - If
CanBeHeldWeakly (key) isfalse , throw aTypeError exception. - For each
Record { [[Key]], [[Value]] } p of M.[[WeakMapData]], do- If p.[[Key]] is not
empty andSameValue (p.[[Key]], key) istrue , then- Set p.[[Value]] to value.
- Return M.
- If p.[[Key]] is not
- Let p be the
Record { [[Key]]: key, [[Value]]: value }. - Append p to M.[[WeakMapData]].
- Return M.
24.3.3.6 WeakMap.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
24.3.4 Properties of WeakMap Instances
WeakMap instances are
24.4 WeakSet Objects
WeakSets are collections of objects and/or symbols. A distinct object or symbol may only occur once
as an element of a WeakSet's collection. A WeakSet may be queried to see if it contains a specific
value, but no mechanism is provided for enumerating the values it holds. In certain conditions,
values which are not
An implementation may impose an arbitrarily determined latency between the time a value contained in a WeakSet becomes inaccessible and the time when the value is removed from the WeakSet. If this latency was observable to ECMAScript program, it would be a source of indeterminacy that could impact program execution. For that reason, an ECMAScript implementation must not provide any means to determine if a WeakSet contains a particular value that does not require the observer to present the observed value.
WeakSets must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of elements in the collection. The data structure used in this specification is only intended to describe the required observable semantics of WeakSets. It is not intended to be a viable implementation model.
See the NOTE in
24.4.1 The WeakSet Constructor
The WeakSet
- is %WeakSet%.
- is the initial value of the
"WeakSet" property of theglobal object . - creates and initializes a new WeakSet when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified WeakSet behaviour must include asupercall to the WeakSetconstructor to create and initialize the subclass instance with the internal state necessary to support theWeakSet.prototypebuilt-in methods.
24.4.1.1 WeakSet ( [ iterable ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Let set be ?
OrdinaryCreateFromConstructor (NewTarget,"%WeakSet.prototype%" , « [[WeakSetData]] »). - Set set.[[WeakSetData]] to a new empty
List . - If iterable is either
undefined ornull , return set. - Let adder be ?
Get (set,"add" ). - If
IsCallable (adder) isfalse , throw aTypeError exception. - Let iteratorRecord be ?
GetIterator (iterable,sync ). - Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , return set. - Let status be
Completion (Call (adder, set, « next »)). IfAbruptCloseIterator (status, iteratorRecord).
- Let next be ?
24.4.2 Properties of the WeakSet Constructor
The WeakSet
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
24.4.2.1 WeakSet.prototype
The initial value of WeakSet.prototype is the
This property has the attributes { [[Writable]]:
24.4.3 Properties of the WeakSet Prototype Object
The WeakSet prototype object:
- is %WeakSet.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a [[WeakSetData]] internal slot.
24.4.3.1 WeakSet.prototype.add ( value )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[WeakSetData]]). - If
CanBeHeldWeakly (value) isfalse , throw aTypeError exception. - For each element e of S.[[WeakSetData]], do
- If e is not
empty andSameValue (e, value) istrue , then- Return S.
- If e is not
- Append value to S.[[WeakSetData]].
- Return S.
24.4.3.2 WeakSet.prototype.constructor
The initial value of WeakSet.prototype.constructor is
24.4.3.3 WeakSet.prototype.delete ( value )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[WeakSetData]]). - If
CanBeHeldWeakly (value) isfalse , returnfalse . - For each element e of S.[[WeakSetData]], do
- If e is not
empty andSameValue (e, value) istrue , then- Replace the element of S.[[WeakSetData]] whose value is e
with an element whose value is
empty . - Return
true .
- Replace the element of S.[[WeakSetData]] whose value is e
with an element whose value is
- If e is not
- Return
false .
The value
24.4.3.4 WeakSet.prototype.has ( value )
This method performs the following steps when called:
- Let S be the
this value. - Perform ?
RequireInternalSlot (S, [[WeakSetData]]). - If
CanBeHeldWeakly (value) isfalse , returnfalse . - For each element e of S.[[WeakSetData]], do
- If e is not
empty andSameValue (e, value) istrue , returntrue .
- If e is not
- Return
false .
24.4.3.5 WeakSet.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
24.4.4 Properties of WeakSet Instances
WeakSet instances are
24.5 Abstract Operations for Keyed Collections
24.5.1 CanonicalizeKeyedCollectionKey ( key )
The abstract operation CanonicalizeKeyedCollectionKey takes argument key (an
- If key is
-0 𝔽, return+0 𝔽. - Return key.
25 Structured Data
25.1 ArrayBuffer Objects
25.1.1 Notation
The descriptions below in this section,
A read-modify-write
modification function is a mathematical function that is represented as an abstract
closure that takes two
- They perform all their algorithm steps atomically.
- Their individual algorithm steps are not observable.
To aid verifying that a read-modify-write modification function's algorithm steps constitute a pure, mathematical function, the following editorial conventions are recommended:
- They do not access, directly or transitively via invoked
abstract operations and abstract closures, any language or specification values except their parameters and captured values. - They do not invoke, directly or transitively,
abstract operations and abstract closures that returnCompletion Records . - They do not return
Completion Records .
25.1.2 Fixed-length and Resizable ArrayBuffer Objects
A fixed-length ArrayBuffer is an ArrayBuffer whose byte length cannot change after creation.
A resizable ArrayBuffer is an ArrayBuffer whose byte length may change
after creation via calls to
The kind of ArrayBuffer object that is created depends on the arguments passed to
25.1.3 Abstract Operations For ArrayBuffer Objects
25.1.3.1 AllocateArrayBuffer ( constructor, byteLength [ , maxByteLength ] )
The abstract operation AllocateArrayBuffer takes arguments constructor (a
- Let slots be « [[ArrayBufferData]], [[ArrayBufferByteLength]], [[ArrayBufferDetachKey]] ».
- If maxByteLength is present and maxByteLength is not
empty , let allocatingResizableBuffer betrue ; otherwise let allocatingResizableBuffer befalse . - If allocatingResizableBuffer is
true , then- If byteLength > maxByteLength, throw a
RangeError exception. - Append [[ArrayBufferMaxByteLength]] to slots.
- If byteLength > maxByteLength, throw a
- Let obj be ?
OrdinaryCreateFromConstructor (constructor,"%ArrayBuffer.prototype%" , slots). - Let block be ?
CreateByteDataBlock (byteLength). - Set obj.[[ArrayBufferData]] to block.
- Set obj.[[ArrayBufferByteLength]] to byteLength.
- If allocatingResizableBuffer is
true , then- If it is not possible to create a
Data Block block consisting of maxByteLength bytes, throw aRangeError exception. - NOTE: Resizable ArrayBuffers are designed to be implementable with in-place growth. Implementations may throw if, for example, virtual memory cannot be reserved up front.
- Set obj.[[ArrayBufferMaxByteLength]] to maxByteLength.
- If it is not possible to create a
- Return obj.
25.1.3.2 ArrayBufferByteLength ( arrayBuffer, order )
The abstract operation ArrayBufferByteLength takes arguments arrayBuffer (an
ArrayBuffer or SharedArrayBuffer) and order (
- If
IsSharedArrayBuffer (arrayBuffer) istrue and arrayBuffer has an [[ArrayBufferByteLengthData]] internal slot, then- Let bufferByteLengthBlock be arrayBuffer.[[ArrayBufferByteLengthData]].
- Let rawLength be
GetRawBytesFromSharedBlock (bufferByteLengthBlock, 0,biguint64 ,true , order). - Let isLittleEndian be the value of the [[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Return
ℝ (RawBytesToNumeric (biguint64 , rawLength, isLittleEndian)).
Assert :IsDetachedBuffer (arrayBuffer) isfalse .- Return arrayBuffer.[[ArrayBufferByteLength]].
25.1.3.3 ArrayBufferCopyAndDetach ( arrayBuffer, newLength, preserveResizability )
The abstract operation ArrayBufferCopyAndDetach takes arguments arrayBuffer (an
- Perform ?
RequireInternalSlot (arrayBuffer, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (arrayBuffer) istrue , throw aTypeError exception. - If newLength is
undefined , then- Let newByteLength be arrayBuffer.[[ArrayBufferByteLength]].
- Else,
- Let newByteLength be ?
ToIndex (newLength).
- Let newByteLength be ?
- If
IsDetachedBuffer (arrayBuffer) istrue , throw aTypeError exception. - If preserveResizability is
preserve-resizability andIsFixedLengthArrayBuffer (arrayBuffer) isfalse , then- Let newMaxByteLength be arrayBuffer.[[ArrayBufferMaxByteLength]].
- Else,
- Let newMaxByteLength be
empty .
- Let newMaxByteLength be
- If arrayBuffer.[[ArrayBufferDetachKey]] is not
undefined , throw aTypeError exception. - Let newBuffer be ?
AllocateArrayBuffer (%ArrayBuffer% , newByteLength, newMaxByteLength). - Let copyLength be
min (newByteLength, arrayBuffer.[[ArrayBufferByteLength]]). - Let fromBlock be arrayBuffer.[[ArrayBufferData]].
- Let toBlock be newBuffer.[[ArrayBufferData]].
- Perform
CopyDataBlockBytes (toBlock, 0, fromBlock, 0, copyLength). - NOTE: Neither creation of the new
Data Block nor copying from the oldData Block are observable. Implementations may implement this method as a zero-copy move or arealloc. - Perform !
DetachArrayBuffer (arrayBuffer). - Return newBuffer.
25.1.3.4 IsDetachedBuffer ( arrayBuffer )
The abstract operation IsDetachedBuffer takes argument arrayBuffer (an ArrayBuffer or a SharedArrayBuffer) and returns a Boolean. It performs the following steps when called:
- If arrayBuffer.[[ArrayBufferData]] is
null , returntrue . - Return
false .
25.1.3.5 DetachArrayBuffer ( arrayBuffer [ , key ] )
The abstract operation DetachArrayBuffer takes argument arrayBuffer (an
ArrayBuffer) and optional argument key (anything) and returns either a
Assert :IsSharedArrayBuffer (arrayBuffer) isfalse .- If key is not present, set key to
undefined . - If arrayBuffer.[[ArrayBufferDetachKey]] is not
key, throw a
TypeError exception. - Set arrayBuffer.[[ArrayBufferData]] to
null . - Set arrayBuffer.[[ArrayBufferByteLength]] to 0.
- Return
unused .
Detaching an ArrayBuffer instance disassociates the
25.1.3.6 CloneArrayBuffer ( srcBuffer, srcByteOffset, srcLength )
The abstract operation CloneArrayBuffer takes arguments srcBuffer (an ArrayBuffer
or a SharedArrayBuffer), srcByteOffset (a non-negative
Assert :IsDetachedBuffer (srcBuffer) isfalse .- Let targetBuffer be ?
AllocateArrayBuffer (%ArrayBuffer% , srcLength). - Let srcBlock be srcBuffer.[[ArrayBufferData]].
- Let targetBlock be targetBuffer.[[ArrayBufferData]].
- Perform
CopyDataBlockBytes (targetBlock, 0, srcBlock, srcByteOffset, srcLength). - Return targetBuffer.
25.1.3.7 GetArrayBufferMaxByteLengthOption ( options )
The abstract operation GetArrayBufferMaxByteLengthOption takes argument options
(an
- If options
is not an Object , returnempty . - Let maxByteLength be ?
Get (options,"maxByteLength" ). - If maxByteLength is
undefined , returnempty . - Return ?
ToIndex (maxByteLength).
25.1.3.8 HostResizeArrayBuffer ( buffer, newByteLength )
The
The implementation of HostResizeArrayBuffer must conform to the following requirements:
- The abstract operation does not detach buffer.
- If the abstract operation completes normally with
handled , buffer.[[ArrayBufferByteLength]] is newByteLength.
The default implementation of HostResizeArrayBuffer is to return
25.1.3.9 IsFixedLengthArrayBuffer ( arrayBuffer )
The abstract operation IsFixedLengthArrayBuffer takes argument arrayBuffer (an ArrayBuffer or a SharedArrayBuffer) and returns a Boolean. It performs the following steps when called:
- If arrayBuffer has an [[ArrayBufferMaxByteLength]] internal slot, return
false . - Return
true .
25.1.3.10 IsUnsignedElementType ( type )
The abstract operation IsUnsignedElementType takes argument type (a
- If type is one of
uint8 ,uint8clamped ,uint16 ,uint32 , orbiguint64 , returntrue . - Return
false .
25.1.3.11 IsUnclampedIntegerElementType ( type )
The abstract operation IsUnclampedIntegerElementType takes argument type (a
- If type is one of
int8 ,uint8 ,int16 ,uint16 ,int32 , oruint32 , returntrue . - Return
false .
25.1.3.12 IsBigIntElementType ( type )
The abstract operation IsBigIntElementType takes argument type (a
- If type is either
biguint64 orbigint64 , returntrue . - Return
false .
25.1.3.13 IsNoTearConfiguration ( type, order )
The abstract operation IsNoTearConfiguration takes arguments type (a
- If
IsUnclampedIntegerElementType (type) istrue , returntrue . - If
IsBigIntElementType (type) istrue and order is neitherinit norunordered , returntrue . - Return
false .
25.1.3.14 RawBytesToNumeric ( type, rawBytes, isLittleEndian )
The abstract operation RawBytesToNumeric takes arguments type (a
- Let elementSize be the Element Size value specified in
Table 75 for Element Type type. - If isLittleEndian is
false , reverse the order of the elements of rawBytes. - If type is
float16 , then- Let value be the byte elements of rawBytes
concatenated and interpreted as a little-endian bit string encoding of an
IEEE 754-2019 binary16 value. - If value is a NaN, return
NaN . - Return the Number value that corresponds to value.
- Let value be the byte elements of rawBytes
concatenated and interpreted as a little-endian bit string encoding of an
- If type is
float32 , then- Let value be the byte elements of rawBytes
concatenated and interpreted as a little-endian bit string encoding of an
IEEE 754-2019 binary32 value. - If value is a NaN, return
NaN . - Return the Number value that corresponds to value.
- Let value be the byte elements of rawBytes
concatenated and interpreted as a little-endian bit string encoding of an
- If type is
float64 , then- Let value be the byte elements of rawBytes
concatenated and interpreted as a little-endian bit string encoding of an
IEEE 754-2019 binary64 value. - If value is a NaN, return
NaN . - Return the Number value that corresponds to value.
- Let value be the byte elements of rawBytes
concatenated and interpreted as a little-endian bit string encoding of an
- If
IsUnsignedElementType (type) istrue , then- Let intValue be the byte elements of rawBytes concatenated and interpreted as a bit string encoding of an unsigned little-endian binary number.
- Else,
- Let intValue be the byte elements of rawBytes concatenated and interpreted as a bit string encoding of a binary little-endian two's complement number of bit length elementSize × 8.
- If
IsBigIntElementType (type) istrue , return the BigInt value that corresponds to intValue. - Otherwise, return the Number value that corresponds to intValue.
25.1.3.15 GetRawBytesFromSharedBlock ( block, byteIndex, type, isTypedArray, order )
The abstract operation GetRawBytesFromSharedBlock takes arguments block (a
- Let elementSize be the Element Size value specified in
Table 75 for Element Type type. - Let execution be the [[CandidateExecution]]
field of the
surrounding agent 'sAgent Record . - Let eventsRecord be the
Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] isAgentSignifier (). - If isTypedArray is
true andIsNoTearConfiguration (type, order) istrue , let noTear betrue ; otherwise let noTear befalse . - Let rawValue be a
List of length elementSize whose elements are nondeterministically chosenbyte values . - NOTE: In implementations, rawValue is the result of a non-atomic or
atomic read instruction on the underlying hardware. The nondeterminism is a semantic
prescription of the
memory model to describe observable behaviour of hardware with weak consistency. - Let readEvent be
ReadSharedMemory { [[Order]]: order, [[NoTear]]: noTear, [[Block]]: block, [[ByteIndex]]: byteIndex, [[ElementSize]]: elementSize }. - Append readEvent to eventsRecord.[[EventList]].
- Append
Chosen Value Record { [[Event]]: readEvent, [[ChosenValue]]: rawValue } to execution.[[ChosenValues]]. - Return rawValue.
25.1.3.16 GetValueFromBuffer ( arrayBuffer, byteIndex, type, isTypedArray, order [ , isLittleEndian ] )
The abstract operation GetValueFromBuffer takes arguments arrayBuffer (an
ArrayBuffer or SharedArrayBuffer), byteIndex (a non-negative
Assert :IsDetachedBuffer (arrayBuffer) isfalse .Assert : There are sufficient bytes in arrayBuffer starting at byteIndex to represent a value of type.- Let block be arrayBuffer.[[ArrayBufferData]].
- Let elementSize be the Element Size value specified in
Table 75 for Element Type type. - If
IsSharedArrayBuffer (arrayBuffer) istrue , thenAssert : block is aShared Data Block .- Let rawValue be
GetRawBytesFromSharedBlock (block, byteIndex, type, isTypedArray, order).
- Else,
Assert : The number of elements in rawValue is elementSize.- If isLittleEndian is not present, set isLittleEndian to the
value of the [[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Return
RawBytesToNumeric (type, rawValue, isLittleEndian).
25.1.3.17 NumericToRawBytes ( type, value, isLittleEndian )
The abstract operation NumericToRawBytes takes arguments type (a
- If type is
float16 , then- Let rawBytes be a
List whose elements are the 2 bytes that are the result of converting value toIEEE 754-2019 binary16 format using roundTiesToEven mode. The bytes are arranged in little endian order. If value isNaN , rawBytes may be set to any implementation chosenIEEE 754-2019 binary16 format NaN encoding. An implementation must always choose the same encoding for each implementation distinguishableNaN value.
- Let rawBytes be a
- Else if type is
float32 , then- Let rawBytes be a
List whose elements are the 4 bytes that are the result of converting value toIEEE 754-2019 binary32 format using roundTiesToEven mode. The bytes are arranged in little endian order. If value isNaN , rawBytes may be set to any implementation chosenIEEE 754-2019 binary32 format NaN encoding. An implementation must always choose the same encoding for each implementation distinguishableNaN value.
- Let rawBytes be a
- Else if type is
float64 , then- Let rawBytes be a
List whose elements are the 8 bytes that are theIEEE 754-2019 binary64 format encoding of value. The bytes are arranged in little endian order. If value isNaN , rawBytes may be set to any implementation chosenIEEE 754-2019 binary64 format NaN encoding. An implementation must always choose the same encoding for each implementation distinguishableNaN value.
- Let rawBytes be a
- Else,
- Let n be the Element Size value specified in
Table 75 for Element Type type. - Let conversionOperation be the abstract operation named in the
Conversion Operation column in
Table 75 for Element Type type. - Let intValue be
ℝ (! conversionOperation(value)). - If intValue ≥ 0, then
- Let rawBytes be a
List whose elements are the n-byte binary encoding of intValue. The bytes are ordered in little endian order.
- Let rawBytes be a
- Else,
- Let rawBytes be a
List whose elements are the n-byte binary two's complement encoding of intValue. The bytes are ordered in little endian order.
- Let rawBytes be a
- Let n be the Element Size value specified in
- If isLittleEndian is
false , reverse the order of the elements of rawBytes. - Return rawBytes.
25.1.3.18 SetValueInBuffer ( arrayBuffer, byteIndex, type, value, isTypedArray, order [ , isLittleEndian ] )
The abstract operation SetValueInBuffer takes arguments arrayBuffer (an
ArrayBuffer or SharedArrayBuffer), byteIndex (a non-negative
Assert :IsDetachedBuffer (arrayBuffer) isfalse .Assert : There are sufficient bytes in arrayBuffer starting at byteIndex to represent a value of type.Assert : valueis a BigInt ifIsBigIntElementType (type) istrue ; otherwise, valueis a Number .- Let block be arrayBuffer.[[ArrayBufferData]].
- Let elementSize be the Element Size value specified in
Table 75 for Element Type type. - If isLittleEndian is not present, set isLittleEndian to the
value of the [[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Let rawBytes be
NumericToRawBytes (type, value, isLittleEndian). - If
IsSharedArrayBuffer (arrayBuffer) istrue , then- Let execution be the [[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - Let eventsRecord be the
Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] isAgentSignifier (). - If isTypedArray is
true andIsNoTearConfiguration (type, order) istrue , let noTear betrue ; otherwise let noTear befalse . - Append
WriteSharedMemory { [[Order]]: order, [[NoTear]]: noTear, [[Block]]: block, [[ByteIndex]]: byteIndex, [[ElementSize]]: elementSize, [[Payload]]: rawBytes } to eventsRecord.[[EventList]].
- Let execution be the [[CandidateExecution]] field of the
- Else,
- Store the individual bytes of rawBytes into block, starting at block[byteIndex].
- Return
unused .
25.1.3.19 GetModifySetValueInBuffer ( arrayBuffer, byteIndex, type, value, op )
The abstract operation GetModifySetValueInBuffer takes arguments arrayBuffer (an
ArrayBuffer or a SharedArrayBuffer), byteIndex (a non-negative
Assert :IsDetachedBuffer (arrayBuffer) isfalse .Assert : There are sufficient bytes in arrayBuffer starting at byteIndex to represent a value of type.Assert : valueis a BigInt ifIsBigIntElementType (type) istrue ; otherwise, valueis a Number .- Let block be arrayBuffer.[[ArrayBufferData]].
- Let elementSize be the Element Size value specified in
Table 75 for Element Type type. - Let isLittleEndian be the value of the [[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Let rawBytes be
NumericToRawBytes (type, value, isLittleEndian). - If
IsSharedArrayBuffer (arrayBuffer) istrue , then- Let execution be the [[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - Let eventsRecord be the
Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] isAgentSignifier (). - Let rawBytesRead be a
List of length elementSize whose elements are nondeterministically chosenbyte values . - NOTE: In implementations, rawBytesRead is the result of a
load-link, of a load-exclusive, or of an operand of a read-modify-write
instruction on the underlying hardware. The nondeterminism is a semantic
prescription of the
memory model to describe observable behaviour of hardware with weak consistency. - Let rmwEvent be
ReadModifyWriteSharedMemory { [[Order]]:seq-cst , [[NoTear]]:true , [[Block]]: block, [[ByteIndex]]: byteIndex, [[ElementSize]]: elementSize, [[Payload]]: rawBytes, [[ModifyOp]]: op }. - Append rmwEvent to eventsRecord.[[EventList]].
- Append
Chosen Value Record { [[Event]]: rmwEvent, [[ChosenValue]]: rawBytesRead } to execution.[[ChosenValues]].
- Let execution be the [[CandidateExecution]] field of the
- Else,
- Let rawBytesRead be a
List of length elementSize whose elements are the sequence of elementSize bytes starting with block[byteIndex]. - Let rawBytesModified be op(rawBytesRead, rawBytes).
- Store the individual bytes of rawBytesModified into block, starting at block[byteIndex].
- Let rawBytesRead be a
- Return
RawBytesToNumeric (type, rawBytesRead, isLittleEndian).
25.1.4 The ArrayBuffer Constructor
The ArrayBuffer
- is %ArrayBuffer%.
- is the initial value of the
"ArrayBuffer" property of theglobal object . - creates and initializes a new ArrayBuffer when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified ArrayBuffer behaviour must include asupercall to the ArrayBufferconstructor to create and initialize subclass instances with the internal state necessary to support theArrayBuffer.prototypebuilt-in methods.
25.1.4.1 ArrayBuffer ( length [ , options ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Let byteLength be ?
ToIndex (length). - Let requestedMaxByteLength be ?
GetArrayBufferMaxByteLengthOption (options). - Return ?
AllocateArrayBuffer (NewTarget, byteLength, requestedMaxByteLength).
25.1.5 Properties of the ArrayBuffer Constructor
The ArrayBuffer
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
25.1.5.1 ArrayBuffer.isView ( arg )
This function performs the following steps when called:
- If arg
is not an Object , returnfalse . - If arg has a [[ViewedArrayBuffer]] internal
slot, return
true . - Return
false .
25.1.5.2 ArrayBuffer.prototype
The initial value of ArrayBuffer.prototype is the
This property has the attributes { [[Writable]]:
25.1.5.3 get ArrayBuffer [ %Symbol.species% ]
ArrayBuffer[%Symbol.species%] is an
- Return the
this value.
The value of the
25.1.6 Properties of the ArrayBuffer Prototype Object
The ArrayBuffer prototype object:
- is %ArrayBuffer.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have an [[ArrayBufferData]] or [[ArrayBufferByteLength]] internal slot.
25.1.6.1 get ArrayBuffer.prototype.byteLength
ArrayBuffer.prototype.byteLength is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - If
IsDetachedBuffer (O) istrue , return+0 𝔽. - Let length be O.[[ArrayBufferByteLength]].
- Return
𝔽 (length).
25.1.6.2 ArrayBuffer.prototype.constructor
The initial value of ArrayBuffer.prototype.constructor is
25.1.6.3 get ArrayBuffer.prototype.detached
ArrayBuffer.prototype.detached is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - Return
IsDetachedBuffer (O).
25.1.6.4 get ArrayBuffer.prototype.maxByteLength
ArrayBuffer.prototype.maxByteLength is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - If
IsDetachedBuffer (O) istrue , return+0 𝔽. - If
IsFixedLengthArrayBuffer (O) istrue , then- Let length be O.[[ArrayBufferByteLength]].
- Else,
- Let length be O.[[ArrayBufferMaxByteLength]].
- Return
𝔽 (length).
25.1.6.5 get ArrayBuffer.prototype.resizable
ArrayBuffer.prototype.resizable is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - If
IsFixedLengthArrayBuffer (O) isfalse , returntrue ; otherwise returnfalse .
25.1.6.6 ArrayBuffer.prototype.resize ( newLength )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferMaxByteLength]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - Let newByteLength be ?
ToIndex (newLength). - If
IsDetachedBuffer (O) istrue , throw aTypeError exception. - If newByteLength > O.[[ArrayBufferMaxByteLength]], throw a
RangeError exception. - Let hostHandled be ?
HostResizeArrayBuffer (O, newByteLength). - If hostHandled is
handled , returnundefined . - Let oldBlock be O.[[ArrayBufferData]].
- Let newBlock be ?
CreateByteDataBlock (newByteLength). - Let copyLength be
min (newByteLength, O.[[ArrayBufferByteLength]]). - Perform
CopyDataBlockBytes (newBlock, 0, oldBlock, 0, copyLength). - NOTE: Neither creation of the new
Data Block nor copying from the oldData Block are observable. Implementations may implement this method as in-place growth or shrinkage. - Set O.[[ArrayBufferData]] to newBlock.
- Set O.[[ArrayBufferByteLength]] to newByteLength.
- Return
undefined .
25.1.6.7 ArrayBuffer.prototype.slice ( start, end )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - If
IsDetachedBuffer (O) istrue , throw aTypeError exception. - Let len be O.[[ArrayBufferByteLength]].
- Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let first be 0.
- Else if relativeStart < 0, let first be
max (len + relativeStart, 0). - Else, let first be
min (relativeStart, len). - If end is
undefined , let relativeEnd be len; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let final be 0.
- Else if relativeEnd < 0, let final be
max (len + relativeEnd, 0). - Else, let final be
min (relativeEnd, len). - Let newLen be
max (final - first, 0). - Let ctor be ?
SpeciesConstructor (O,%ArrayBuffer% ). - Let new be ?
Construct (ctor, «𝔽 (newLen) »). - Perform ?
RequireInternalSlot (new, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (new) istrue , throw aTypeError exception. - If
IsDetachedBuffer (new) istrue , throw aTypeError exception. - If
SameValue (new, O) istrue , throw aTypeError exception. - If new.[[ArrayBufferByteLength]] <
newLen, throw a
TypeError exception. - NOTE: Side-effects of the above steps may have detached or resized O.
- If
IsDetachedBuffer (O) istrue , throw aTypeError exception. - Let fromBuf be O.[[ArrayBufferData]].
- Let toBuf be new.[[ArrayBufferData]].
- Let currentLen be O.[[ArrayBufferByteLength]].
- If first < currentLen, then
- Let count be
min (newLen, currentLen - first). - Perform
CopyDataBlockBytes (toBuf, 0, fromBuf, first, count).
- Let count be
- Return new.
25.1.6.8 ArrayBuffer.prototype.transfer ( [ newLength ] )
This method performs the following steps when called:
- Let O be the
this value. - Return ?
ArrayBufferCopyAndDetach (O, newLength,preserve-resizability ).
25.1.6.9 ArrayBuffer.prototype.transferToFixedLength ( [ newLength ] )
This method performs the following steps when called:
- Let O be the
this value. - Return ?
ArrayBufferCopyAndDetach (O, newLength,fixed-length ).
25.1.6.10 ArrayBuffer.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
25.1.7 Properties of ArrayBuffer Instances
ArrayBuffer instances inherit properties from the
ArrayBuffer instances whose [[ArrayBufferData]] is
ArrayBuffer instances whose [[ArrayBufferDetachKey]] is set to a value
other than
25.1.8 Resizable ArrayBuffer Guidelines
The following are guidelines for ECMAScript programmers working with
We recommend that programs be tested in their deployment environments where possible. The amount of available physical memory differs greatly between hardware devices. Similarly, virtual memory subsystems also differ greatly between hardware devices as well as operating systems. An application that runs without out-of-memory errors on a 64-bit desktop web browser could run out of memory on a 32-bit mobile web browser.
When choosing a value for the
Please note that successfully constructing a
The following are guidelines for ECMAScript implementers implementing
If a
If a
25.2 SharedArrayBuffer Objects
25.2.1 Fixed-length and Growable SharedArrayBuffer Objects
A fixed-length SharedArrayBuffer is a SharedArrayBuffer whose byte length cannot change after creation.
A growable SharedArrayBuffer is a SharedArrayBuffer whose byte length
may increase after creation via calls to
The kind of SharedArrayBuffer object that is created depends on the arguments passed to
25.2.2 Abstract Operations for SharedArrayBuffer Objects
25.2.2.1 AllocateSharedArrayBuffer ( constructor, byteLength [ , maxByteLength ] )
The abstract operation AllocateSharedArrayBuffer takes arguments constructor (a
- Let slots be « [[ArrayBufferData]] ».
- If maxByteLength is present and maxByteLength is not
empty , let allocatingGrowableBuffer betrue ; otherwise let allocatingGrowableBuffer befalse . - If allocatingGrowableBuffer is
true , then- If byteLength > maxByteLength, throw a
RangeError exception. - Append [[ArrayBufferByteLengthData]] and [[ArrayBufferMaxByteLength]] to slots.
- If byteLength > maxByteLength, throw a
- Else,
- Append [[ArrayBufferByteLength]] to slots.
- Let obj be ?
OrdinaryCreateFromConstructor (constructor,"%SharedArrayBuffer.prototype%" , slots). - If allocatingGrowableBuffer is
true , let allocLength be maxByteLength; otherwise let allocLength be byteLength. - Let block be ?
CreateSharedByteDataBlock (allocLength). - Set obj.[[ArrayBufferData]] to block.
- If allocatingGrowableBuffer is
true , thenAssert : byteLength ≤ maxByteLength.- Let byteLengthBlock be ?
CreateSharedByteDataBlock (8). - Perform
SetValueInBuffer (byteLengthBlock, 0,biguint64 ,ℤ (byteLength),true ,seq-cst ). - Set obj.[[ArrayBufferByteLengthData]] to byteLengthBlock.
- Set obj.[[ArrayBufferMaxByteLength]] to maxByteLength.
- Else,
- Set obj.[[ArrayBufferByteLength]] to byteLength.
- Return obj.
25.2.2.2 IsSharedArrayBuffer ( obj )
The abstract operation IsSharedArrayBuffer takes argument obj (an ArrayBuffer or a SharedArrayBuffer) and returns a Boolean. It tests whether an object is an ArrayBuffer, a SharedArrayBuffer, or a subtype of either. It performs the following steps when called:
- Let bufferData be obj.[[ArrayBufferData]].
- If bufferData is
null , returnfalse . - If bufferData is a
Data Block , returnfalse . Assert : bufferData is aShared Data Block .- Return
true .
25.2.2.3 HostGrowSharedArrayBuffer ( buffer, newByteLength )
The
The implementation of HostGrowSharedArrayBuffer must conform to the following requirements:
- If the abstract operation does not complete normally with
unhandled , and newByteLength < the current byte length of the buffer or newByteLength > buffer.[[ArrayBufferMaxByteLength]], throw aRangeError exception. - Let isLittleEndian be the value of the [[LittleEndian]] field of the
surrounding agent 'sAgent Record . If the abstract operation completes normally withhandled , aWriteSharedMemory orReadModifyWriteSharedMemory event whose [[Order]] isseq-cst , [[Payload]] isNumericToRawBytes (biguint64 , newByteLength, isLittleEndian), [[Block]] is buffer.[[ArrayBufferByteLengthData]], [[ByteIndex]] is 0, and [[ElementSize]] is 8 is added to thesurrounding agent 'scandidate execution such that racing calls toSharedArrayBuffer.prototype.groware not "lost", i.e. silently do nothing.
The second requirement above is intentionally vague about how or when the current byte length of buffer is read. Because the byte length must be updated via an atomic read-modify-write operation on the underlying hardware, architectures that use load-link/store-conditional or load-exclusive/store-exclusive instruction pairs may wish to keep the paired instructions close in the instruction stream. As such, SharedArrayBuffer.prototype.grow itself does not perform bounds checking on newByteLength before calling HostGrowSharedArrayBuffer, nor is there a requirement on when the current byte length is read.
This is in contrast with
The default implementation of HostGrowSharedArrayBuffer is to return
25.2.3 The SharedArrayBuffer Constructor
The SharedArrayBuffer
- is %SharedArrayBuffer%.
- is the initial value of the
"SharedArrayBuffer" property of theglobal object , if that property is present (see below). - creates and initializes a new SharedArrayBuffer when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified SharedArrayBuffer behaviour must include asupercall to the SharedArrayBufferconstructor to create and initialize subclass instances with the internal state necessary to support theSharedArrayBuffer.prototypebuilt-in methods.
Whenever a
Unlike an ArrayBuffer, a SharedArrayBuffer cannot become
detached, and its internal [[ArrayBufferData]] slot is never
25.2.3.1 SharedArrayBuffer ( length [ , options ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Let byteLength be ?
ToIndex (length). - Let requestedMaxByteLength be ?
GetArrayBufferMaxByteLengthOption (options). - Return ?
AllocateSharedArrayBuffer (NewTarget, byteLength, requestedMaxByteLength).
25.2.4 Properties of the SharedArrayBuffer Constructor
The SharedArrayBuffer
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
25.2.4.1 SharedArrayBuffer.prototype
The initial value of SharedArrayBuffer.prototype is the
This property has the attributes { [[Writable]]:
25.2.4.2 get SharedArrayBuffer [ %Symbol.species% ]
SharedArrayBuffer[%Symbol.species%] is an
- Return the
this value.
The value of the
25.2.5 Properties of the SharedArrayBuffer Prototype Object
The SharedArrayBuffer prototype object:
- is %SharedArrayBuffer.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have an [[ArrayBufferData]] or [[ArrayBufferByteLength]] internal slot.
25.2.5.1 get SharedArrayBuffer.prototype.byteLength
SharedArrayBuffer.prototype.byteLength is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) isfalse , throw aTypeError exception. - Let length be
ArrayBufferByteLength (O,seq-cst ). - Return
𝔽 (length).
25.2.5.2 SharedArrayBuffer.prototype.constructor
The initial value of SharedArrayBuffer.prototype.constructor is
25.2.5.3 SharedArrayBuffer.prototype.grow ( newLength )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferMaxByteLength]]). - If
IsSharedArrayBuffer (O) isfalse , throw aTypeError exception. - Let newByteLength be ?
ToIndex (newLength). - Let hostHandled be ?
HostGrowSharedArrayBuffer (O, newByteLength). - If hostHandled is
handled , returnundefined . - Let isLittleEndian be the value of the [[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Let byteLengthBlock be O.[[ArrayBufferByteLengthData]].
- Let currentByteLengthRawBytes be
GetRawBytesFromSharedBlock (byteLengthBlock, 0,biguint64 ,true ,seq-cst ). - Let newByteLengthRawBytes be
NumericToRawBytes (biguint64 ,ℤ (newByteLength), isLittleEndian). - Repeat,
- NOTE: This is a compare-and-exchange loop to ensure that parallel, racing grows of the same buffer are totally ordered, are not lost, and do not silently do nothing. The loop exits if it was able to attempt to grow uncontended.
- Let currentByteLength be
ℝ (RawBytesToNumeric (biguint64 , currentByteLengthRawBytes, isLittleEndian)). - If newByteLength = currentByteLength, return
undefined . - If newByteLength < currentByteLength or
newByteLength > O.[[ArrayBufferMaxByteLength]], throw a
RangeError exception. - Let byteLengthDelta be newByteLength - currentByteLength.
- If it is impossible to create a new
Shared Data Block value consisting of byteLengthDelta bytes, throw aRangeError exception. - NOTE: No new
Shared Data Block is constructed and used here. The observable behaviour of growable SharedArrayBuffers is specified by allocating amax -sizedShared Data Block at construction time, and this step captures the requirement that implementations that run out of memory must throw aRangeError . - Let readByteLengthRawBytes be
AtomicCompareExchangeInSharedBlock (byteLengthBlock, 0, 8, currentByteLengthRawBytes, newByteLengthRawBytes). - If
ByteListEqual (readByteLengthRawBytes, currentByteLengthRawBytes) istrue , returnundefined . - Set currentByteLengthRawBytes to readByteLengthRawBytes.
Spurious failures of the compare-exchange to update the length are prohibited. If the
bounds checking for the new length passes and the implementation is not out of
memory, a
Parallel calls to SharedArrayBuffer.prototype.grow are totally ordered. For example,
consider two racing calls: sab.grow(10) and sab.grow(20).
One of the two calls is guaranteed to win the race. The call to
sab.grow(10) will never shrink sab even if
sab.grow(20) happened first; in that case it will instead throw a
RangeError.
25.2.5.4 get SharedArrayBuffer.prototype.growable
SharedArrayBuffer.prototype.growable is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) isfalse , throw aTypeError exception. - If
IsFixedLengthArrayBuffer (O) isfalse , returntrue ; otherwise returnfalse .
25.2.5.5 get SharedArrayBuffer.prototype.maxByteLength
SharedArrayBuffer.prototype.maxByteLength is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) isfalse , throw aTypeError exception. - If
IsFixedLengthArrayBuffer (O) istrue , then- Let length be O.[[ArrayBufferByteLength]].
- Else,
- Let length be O.[[ArrayBufferMaxByteLength]].
- Return
𝔽 (length).
25.2.5.6 SharedArrayBuffer.prototype.slice ( start, end )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) isfalse , throw aTypeError exception. - Let len be
ArrayBufferByteLength (O,seq-cst ). - Let relativeStart be ?
ToIntegerOrInfinity (start). - If relativeStart = -∞, let first be 0.
- Else if relativeStart < 0, let first be
max (len + relativeStart, 0). - Else, let first be
min (relativeStart, len). - If end is
undefined , let relativeEnd be len; else let relativeEnd be ?ToIntegerOrInfinity (end). - If relativeEnd = -∞, let final be 0.
- Else if relativeEnd < 0, let final be
max (len + relativeEnd, 0). - Else, let final be
min (relativeEnd, len). - Let newLen be
max (final - first, 0). - Let ctor be ?
SpeciesConstructor (O,%SharedArrayBuffer% ). - Let new be ?
Construct (ctor, «𝔽 (newLen) »). - Perform ?
RequireInternalSlot (new, [[ArrayBufferData]]). - If
IsSharedArrayBuffer (new) isfalse , throw aTypeError exception. - If new.[[ArrayBufferData]] is O.[[ArrayBufferData]], throw a
TypeError exception. - If
ArrayBufferByteLength (new,seq-cst ) < newLen, throw aTypeError exception. - Let fromBuf be O.[[ArrayBufferData]].
- Let toBuf be new.[[ArrayBufferData]].
- Perform
CopyDataBlockBytes (toBuf, 0, fromBuf, first, newLen). - Return new.
25.2.5.7 SharedArrayBuffer.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
25.2.6 Properties of SharedArrayBuffer Instances
SharedArrayBuffer instances inherit properties from the
SharedArrayBuffer instances, unlike ArrayBuffer instances, are never detached.
25.2.7 Growable SharedArrayBuffer Guidelines
The following are guidelines for ECMAScript programmers working with
We recommend that programs be tested in their deployment environments where possible. The amount of available physical memory differ greatly between hardware devices. Similarly, virtual memory subsystems also differ greatly between hardware devices as well as operating systems. An application that runs without out-of-memory errors on a 64-bit desktop web browser could run out of memory on a 32-bit mobile web browser.
When choosing a value for the
Please note that successfully constructing a
Not all loads of a u8[idx], are not synchronizing. In general, in the absence of explicit
synchronization, one property access being in-bound does not imply a subsequent property
access in the same length and byteLength getters on
SharedArrayBuffer,
The following are guidelines for ECMAScript implementers implementing
We recommend
Because grow operations can happen in parallel with memory accesses on a
Grown memory must appear zeroed from the moment of its creation, including to any racy accesses in parallel. This can be accomplished via zero-filled-on-demand virtual memory pages, or careful synchronization if manually zeroing memory.
In practice it is difficult to implement
25.3 DataView Objects
25.3.1 Abstract Operations For DataView Objects
25.3.1.1 DataView With Buffer Witness Records
A DataView With Buffer
Witness Record is a
DataView With Buffer Witness Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Object]] | a DataView | The DataView object whose buffer's byte length is loaded. |
| [[CachedBufferByteLength]] |
a non-negative |
The byte length of the object's [[ViewedArrayBuffer]] when the |
25.3.1.2 MakeDataViewWithBufferWitnessRecord ( obj, order )
The abstract operation MakeDataViewWithBufferWitnessRecord takes arguments obj (a
DataView) and order (
- Let buffer be obj.[[ViewedArrayBuffer]].
- If
IsDetachedBuffer (buffer) istrue , then- Let byteLength be
detached .
- Let byteLength be
- Else,
- Let byteLength be
ArrayBufferByteLength (buffer, order).
- Let byteLength be
- Return the
DataView With Buffer Witness Record { [[Object]]: obj, [[CachedBufferByteLength]]: byteLength }.
25.3.1.3 GetViewByteLength ( viewRecord )
The abstract operation GetViewByteLength takes argument viewRecord (a
Assert :IsViewOutOfBounds (viewRecord) isfalse .- Let view be viewRecord.[[Object]].
- If view.[[ByteLength]] is not
auto , return view.[[ByteLength]]. Assert :IsFixedLengthArrayBuffer (view.[[ViewedArrayBuffer]]) isfalse .- Let byteOffset be view.[[ByteOffset]].
- Let byteLength be viewRecord.[[CachedBufferByteLength]].
Assert : byteLength is notdetached .- Return byteLength - byteOffset.
25.3.1.4 IsViewOutOfBounds ( viewRecord )
The abstract operation IsViewOutOfBounds takes argument viewRecord (a
- Let view be viewRecord.[[Object]].
- Let bufferByteLength be viewRecord.[[CachedBufferByteLength]].
Assert :IsDetachedBuffer (view.[[ViewedArrayBuffer]]) istrue if and only if bufferByteLength isdetached .- If bufferByteLength is
detached , returntrue . - Let byteOffsetStart be view.[[ByteOffset]].
- If view.[[ByteLength]] is
auto , then- Let byteOffsetEnd be bufferByteLength.
- Else,
- Let byteOffsetEnd be byteOffsetStart + view.[[ByteLength]].
- If byteOffsetStart > bufferByteLength or
byteOffsetEnd > bufferByteLength, return
true . - NOTE: 0-length DataViews are not considered out-of-bounds.
- Return
false .
25.3.1.5 GetViewValue ( view, requestIndex, isLittleEndian, type )
The abstract operation GetViewValue takes arguments view (an
- Perform ?
RequireInternalSlot (view, [[DataView]]). Assert : view has a [[ViewedArrayBuffer]] internal slot.- Let getIndex be ?
ToIndex (requestIndex). - Set isLittleEndian to
ToBoolean (isLittleEndian). - Let viewOffset be view.[[ByteOffset]].
- Let viewRecord be
MakeDataViewWithBufferWitnessRecord (view,unordered ). - NOTE: Bounds checking is not a synchronizing operation when view's
backing buffer is a
growable SharedArrayBuffer . - If
IsViewOutOfBounds (viewRecord) istrue , throw aTypeError exception. - Let viewSize be
GetViewByteLength (viewRecord). - Let elementSize be the Element Size value specified in
Table 75 for Element Type type. - If getIndex + elementSize > viewSize, throw a
RangeError exception. - Let bufferIndex be getIndex + viewOffset.
- Return
GetValueFromBuffer (view.[[ViewedArrayBuffer]], bufferIndex, type,false ,unordered , isLittleEndian).
25.3.1.6 SetViewValue ( view, requestIndex, isLittleEndian, type, value )
The abstract operation SetViewValue takes arguments view (an
- Perform ?
RequireInternalSlot (view, [[DataView]]). Assert : view has a [[ViewedArrayBuffer]] internal slot.- Let getIndex be ?
ToIndex (requestIndex). - If
IsBigIntElementType (type) istrue , let numberValue be ?ToBigInt (value). - Otherwise, let numberValue be ?
ToNumber (value). - Set isLittleEndian to
ToBoolean (isLittleEndian). - Let viewOffset be view.[[ByteOffset]].
- Let viewRecord be
MakeDataViewWithBufferWitnessRecord (view,unordered ). - NOTE: Bounds checking is not a synchronizing operation when view's
backing buffer is a
growable SharedArrayBuffer . - If
IsViewOutOfBounds (viewRecord) istrue , throw aTypeError exception. - Let viewSize be
GetViewByteLength (viewRecord). - Let elementSize be the Element Size value specified in
Table 75 for Element Type type. - If getIndex + elementSize > viewSize, throw a
RangeError exception. - Let bufferIndex be getIndex + viewOffset.
- Perform
SetValueInBuffer (view.[[ViewedArrayBuffer]], bufferIndex, type, numberValue,false ,unordered , isLittleEndian). - Return
undefined .
25.3.2 The DataView Constructor
The DataView
- is %DataView%.
- is the initial value of the
"DataView" property of theglobal object . - creates and initializes a new DataView when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified DataView behaviour must include asupercall to the DataViewconstructor to create and initialize subclass instances with the internal state necessary to support theDataView.prototypebuilt-in methods.
25.3.2.1 DataView ( buffer [ , byteOffset [ , byteLength ] ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Perform ?
RequireInternalSlot (buffer, [[ArrayBufferData]]). - Let offset be ?
ToIndex (byteOffset). - If
IsDetachedBuffer (buffer) istrue , throw aTypeError exception. - Let bufferByteLength be
ArrayBufferByteLength (buffer,seq-cst ). - If offset > bufferByteLength, throw a
RangeError exception. - Let bufferIsFixedLength be
IsFixedLengthArrayBuffer (buffer). - If byteLength is
undefined , then- If bufferIsFixedLength is
true , then- Let viewByteLength be bufferByteLength - offset.
- Else,
- Let viewByteLength be
auto .
- Let viewByteLength be
- If bufferIsFixedLength is
- Else,
- Let viewByteLength be ?
ToIndex (byteLength). - If offset + viewByteLength >
bufferByteLength, throw a
RangeError exception.
- Let viewByteLength be ?
- Let O be ?
OrdinaryCreateFromConstructor (NewTarget,"%DataView.prototype%" , « [[DataView]], [[ViewedArrayBuffer]], [[ByteLength]], [[ByteOffset]] »). - If
IsDetachedBuffer (buffer) istrue , throw aTypeError exception. - Set bufferByteLength to
ArrayBufferByteLength (buffer,seq-cst ). - If offset > bufferByteLength, throw a
RangeError exception. - If byteLength is not
undefined , then- If offset + viewByteLength >
bufferByteLength, throw a
RangeError exception.
- If offset + viewByteLength >
bufferByteLength, throw a
- Set O.[[ViewedArrayBuffer]] to buffer.
- Set O.[[ByteLength]] to viewByteLength.
- Set O.[[ByteOffset]] to offset.
- Return O.
25.3.3 Properties of the DataView Constructor
The DataView
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
25.3.3.1 DataView.prototype
The initial value of DataView.prototype is the
This property has the attributes { [[Writable]]:
25.3.4 Properties of the DataView Prototype Object
The DataView prototype object:
- is %DataView.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a [[DataView]], [[ViewedArrayBuffer]], [[ByteLength]], or [[ByteOffset]] internal slot.
25.3.4.1 get DataView.prototype.buffer
DataView.prototype.buffer is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[DataView]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let buffer be O.[[ViewedArrayBuffer]].
- Return buffer.
25.3.4.2 get DataView.prototype.byteLength
DataView.prototype.byteLength is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[DataView]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let viewRecord be
MakeDataViewWithBufferWitnessRecord (O,seq-cst ). - If
IsViewOutOfBounds (viewRecord) istrue , throw aTypeError exception. - Let size be
GetViewByteLength (viewRecord). - Return
𝔽 (size).
25.3.4.3 get DataView.prototype.byteOffset
DataView.prototype.byteOffset is an
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[DataView]]). Assert : O has a [[ViewedArrayBuffer]] internal slot.- Let viewRecord be
MakeDataViewWithBufferWitnessRecord (O,seq-cst ). - If
IsViewOutOfBounds (viewRecord) istrue , throw aTypeError exception. - Let offset be O.[[ByteOffset]].
- Return
𝔽 (offset).
25.3.4.4 DataView.prototype.constructor
The initial value of DataView.prototype.constructor is
25.3.4.5 DataView.prototype.getBigInt64 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - Return ?
GetViewValue (view, byteOffset, littleEndian,bigint64 ).
25.3.4.6 DataView.prototype.getBigUint64 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - Return ?
GetViewValue (view, byteOffset, littleEndian,biguint64 ).
25.3.4.7 DataView.prototype.getFloat16 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - If littleEndian is not present, set littleEndian to
false . - Return ?
GetViewValue (view, byteOffset, littleEndian,float16 ).
25.3.4.8 DataView.prototype.getFloat32 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - If littleEndian is not present, set littleEndian to
false . - Return ?
GetViewValue (view, byteOffset, littleEndian,float32 ).
25.3.4.9 DataView.prototype.getFloat64 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - If littleEndian is not present, set littleEndian to
false . - Return ?
GetViewValue (view, byteOffset, littleEndian,float64 ).
25.3.4.10 DataView.prototype.getInt8 ( byteOffset )
This method performs the following steps when called:
- Let view be the
this value. - Return ?
GetViewValue (view, byteOffset,true ,int8 ).
25.3.4.11 DataView.prototype.getInt16 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - If littleEndian is not present, set littleEndian to
false . - Return ?
GetViewValue (view, byteOffset, littleEndian,int16 ).
25.3.4.12 DataView.prototype.getInt32 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - If littleEndian is not present, set littleEndian to
false . - Return ?
GetViewValue (view, byteOffset, littleEndian,int32 ).
25.3.4.13 DataView.prototype.getUint8 ( byteOffset )
This method performs the following steps when called:
- Let view be the
this value. - Return ?
GetViewValue (view, byteOffset,true ,uint8 ).
25.3.4.14 DataView.prototype.getUint16 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - If littleEndian is not present, set littleEndian to
false . - Return ?
GetViewValue (view, byteOffset, littleEndian,uint16 ).
25.3.4.15 DataView.prototype.getUint32 ( byteOffset [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - If littleEndian is not present, set littleEndian to
false . - Return ?
GetViewValue (view, byteOffset, littleEndian,uint32 ).
25.3.4.16 DataView.prototype.setBigInt64 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - Return ?
SetViewValue (view, byteOffset, littleEndian,bigint64 , value).
25.3.4.17 DataView.prototype.setBigUint64 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - Return ?
SetViewValue (view, byteOffset, littleEndian,biguint64 , value).
25.3.4.18 DataView.prototype.setFloat16 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - If littleEndian is not present, set littleEndian to
false . - Return ?
SetViewValue (view, byteOffset, littleEndian,float16 , value).
25.3.4.19 DataView.prototype.setFloat32 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - If littleEndian is not present, set littleEndian to
false . - Return ?
SetViewValue (view, byteOffset, littleEndian,float32 , value).
25.3.4.20 DataView.prototype.setFloat64 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - If littleEndian is not present, set littleEndian to
false . - Return ?
SetViewValue (view, byteOffset, littleEndian,float64 , value).
25.3.4.21 DataView.prototype.setInt8 ( byteOffset, value )
This method performs the following steps when called:
- Let view be the
this value. - Return ?
SetViewValue (view, byteOffset,true ,int8 , value).
25.3.4.22 DataView.prototype.setInt16 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - If littleEndian is not present, set littleEndian to
false . - Return ?
SetViewValue (view, byteOffset, littleEndian,int16 , value).
25.3.4.23 DataView.prototype.setInt32 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - If littleEndian is not present, set littleEndian to
false . - Return ?
SetViewValue (view, byteOffset, littleEndian,int32 , value).
25.3.4.24 DataView.prototype.setUint8 ( byteOffset, value )
This method performs the following steps when called:
- Let view be the
this value. - Return ?
SetViewValue (view, byteOffset,true ,uint8 , value).
25.3.4.25 DataView.prototype.setUint16 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - If littleEndian is not present, set littleEndian to
false . - Return ?
SetViewValue (view, byteOffset, littleEndian,uint16 , value).
25.3.4.26 DataView.prototype.setUint32 ( byteOffset, value [ , littleEndian ] )
This method performs the following steps when called:
- Let view be the
this value. - If littleEndian is not present, set littleEndian to
false . - Return ?
SetViewValue (view, byteOffset, littleEndian,uint32 , value).
25.3.4.27 DataView.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
25.3.5 Properties of DataView Instances
DataView instances are
The value of the [[DataView]] internal slot is not used within
this specification. The simple presence of that internal slot is used within the
specification to identify objects created using the DataView
25.4 The Atomics Object
The Atomics object:
- is %Atomics%.
- is the initial value of the
"Atomics" property of theglobal object . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Object.prototype% . - does not have a [[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a [[Call]] internal method; it cannot be invoked as a function.
The Atomics object provides functions that operate indivisibly (atomically) on shared memory array
cells as well as functions that let
For informative guidelines for programming and implementing shared memory in ECMAScript,
please see the notes at the end of the
25.4.1 Waiter Record
A Waiter Record is a Atomics.wait or Atomics.waitAsync.
A Waiter Record has fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[AgentSignifier]] |
an |
The Atomics.wait or Atomics.waitAsync.
|
| [[PromiseCapability]] |
a |
If denoting a call to Atomics.waitAsync, the resulting promise,
otherwise |
| [[TimeoutTime]] |
a non-negative |
The earliest time by which timeout may be triggered; computed using
|
| [[Result]] |
|
The return value of the call. |
25.4.2 WaiterList Records
A WaiterList Record is used to explain
waiting and notification of Atomics.wait,
Atomics.waitAsync, and Atomics.notify.
A WaiterList Record has fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Waiters]] |
a |
The calls to Atomics.wait or Atomics.waitAsync
that are waiting on the location with which this WaiterList is associated.
|
| [[MostRecentLeaveEvent]] |
a |
The event of the most recent leaving of its |
There can be multiple
The
Each WaiterList Record has a critical
section that controls exclusive access to that WaiterList Record during evaluation.
Only a single
25.4.3 Abstract Operations for Atomics
25.4.3.1 ValidateIntegerTypedArray ( typedArray, waitable )
The abstract operation ValidateIntegerTypedArray takes arguments typedArray (an
- Let taRecord be ?
ValidateTypedArray (typedArray,unordered ). - NOTE: Bounds checking is not a synchronizing operation when typedArray's
backing buffer is a
growable SharedArrayBuffer . - If waitable is
true , then- If typedArray.[[TypedArrayName]] is
neither
"Int32Array" nor"BigInt64Array" , throw aTypeError exception.
- If typedArray.[[TypedArrayName]] is
neither
- Else,
- Let type be
TypedArrayElementType (typedArray). - If
IsUnclampedIntegerElementType (type) isfalse andIsBigIntElementType (type) isfalse , throw aTypeError exception.
- Let type be
- Return taRecord.
25.4.3.2 ValidateAtomicAccess ( taRecord, requestIndex )
The abstract operation ValidateAtomicAccess takes arguments taRecord (a
- Let length be
TypedArrayLength (taRecord). - Let accessIndex be ?
ToIndex (requestIndex). Assert : accessIndex ≥ 0.- If accessIndex ≥ length, throw a
RangeError exception. - Let typedArray be taRecord.[[Object]].
- Let elementSize be
TypedArrayElementSize (typedArray). - Let offset be typedArray.[[ByteOffset]].
- Return (accessIndex × elementSize) + offset.
25.4.3.3 ValidateAtomicAccessOnIntegerTypedArray ( typedArray, requestIndex )
The abstract operation ValidateAtomicAccessOnIntegerTypedArray takes arguments
typedArray (an
- Let taRecord be ?
ValidateIntegerTypedArray (typedArray,false ). - Return ?
ValidateAtomicAccess (taRecord, requestIndex).
25.4.3.4 RevalidateAtomicAccess ( typedArray, byteIndexInBuffer )
The abstract operation RevalidateAtomicAccess takes arguments typedArray (a
- Let taRecord be
MakeTypedArrayWithBufferWitnessRecord (typedArray,unordered ). - NOTE: Bounds checking is not a synchronizing operation when typedArray's
backing buffer is a
growable SharedArrayBuffer . - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. Assert : byteIndexInBuffer ≥ typedArray.[[ByteOffset]].- If byteIndexInBuffer ≥ taRecord.[[CachedBufferByteLength]], throw a
RangeError exception. - Return
unused .
25.4.3.5 GetWaiterList ( block, i )
The abstract operation GetWaiterList takes arguments block (a
Assert : i and i + 3 are valid byte offsets within the memory of block.- Return the
WaiterList Record that is referenced by the pair (block, i).
25.4.3.6 EnterCriticalSection ( WL )
The abstract operation EnterCriticalSection takes argument WL (a
Assert : Thesurrounding agent is not in thecritical section for anyWaiterList Record .- Wait until no
agent is in thecritical section for WL, then enter thecritical section for WL (without allowing any otheragent to enter). - If WL.[[MostRecentLeaveEvent]] is not
empty , then- NOTE: A WL whose
critical section has been entered at least once has aSynchronize event set byLeaveCriticalSection . - Let execution be the [[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - Let eventsRecord be the
Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] isAgentSignifier (). - Let enterEvent be a new
Synchronize event . - Append enterEvent to eventsRecord.[[EventList]].
- Append (WL.[[MostRecentLeaveEvent]], enterEvent) to eventsRecord.[[AgentSynchronizesWith]].
- NOTE: A WL whose
- Return
unused .
EnterCriticalSection has contention when an
25.4.3.7 LeaveCriticalSection ( WL )
The abstract operation LeaveCriticalSection takes argument WL (a
Assert : Thesurrounding agent is in thecritical section for WL.- Let execution be the [[CandidateExecution]]
field of the
surrounding agent 'sAgent Record . - Let eventsRecord be the
Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] isAgentSignifier (). - Let leaveEvent be a new
Synchronize event . - Append leaveEvent to eventsRecord.[[EventList]].
- Set WL.[[MostRecentLeaveEvent]] to leaveEvent.
- Leave the
critical section for WL. - Return
unused .
25.4.3.8 AddWaiter ( WL, waiterRecord )
The abstract operation AddWaiter takes arguments WL (a
Assert : Thesurrounding agent is in thecritical section for WL.Assert : There is noWaiter Record in WL.[[Waiters]] whose [[PromiseCapability]] field is waiterRecord.[[PromiseCapability]] and whose [[AgentSignifier]] field is waiterRecord.[[AgentSignifier]].- Append waiterRecord to WL.[[Waiters]].
- Return
unused .
25.4.3.9 RemoveWaiter ( WL, waiterRecord )
The abstract operation RemoveWaiter takes arguments WL (a
Assert : Thesurrounding agent is in thecritical section for WL.Assert : WL.[[Waiters]] contains waiterRecord.- Remove waiterRecord from WL.[[Waiters]].
- Return
unused .
25.4.3.10 RemoveWaiters ( WL, c )
The abstract operation RemoveWaiters takes arguments WL (a
Assert : Thesurrounding agent is in thecritical section for WL.- Let len be the number of elements in WL.[[Waiters]].
- Let n be
min (c, len). - Let L be a
List whose elements are the first n elements of WL.[[Waiters]]. - Remove the first n elements of WL.[[Waiters]].
- Return L.
25.4.3.11 SuspendThisAgent ( WL, waiterRecord )
The abstract operation SuspendThisAgent takes arguments WL (a
Assert : Thesurrounding agent is in thecritical section for WL.Assert : WL.[[Waiters]] contains waiterRecord.- Let thisAgent be
AgentSignifier (). Assert : waiterRecord.[[AgentSignifier]] is thisAgent.Assert : waiterRecord.[[PromiseCapability]] isblocking .Assert :AgentCanSuspend () istrue .- Perform
LeaveCriticalSection (WL) and suspend thesurrounding agent until the time is waiterRecord.[[TimeoutTime]], performing the combined operation in such a way that a notification that arrives after thecritical section is exited but before the suspension takes effect is not lost. Thesurrounding agent can only wake from suspension due to a timeout or due to anotheragent callingNotifyWaiter with arguments WL and thisAgent (i.e. via a call toAtomics.notify). - Perform
EnterCriticalSection (WL). - Return
unused .
25.4.3.12 NotifyWaiter ( WL, waiterRecord )
The abstract operation NotifyWaiter takes arguments WL (a
Assert : Thesurrounding agent is in thecritical section for WL.- If waiterRecord.[[PromiseCapability]] is
blocking , then- Wake the
agent whose signifier is waiterRecord.[[AgentSignifier]] from suspension. - NOTE: This causes the
agent to resume execution inSuspendThisAgent .
- Wake the
- Else if
AgentSignifier () is waiterRecord.[[AgentSignifier]], then- Let promiseCapability be waiterRecord.[[PromiseCapability]].
- Perform !
Call (promiseCapability.[[Resolve]],undefined , « waiterRecord.[[Result]] »).
- Else,
- Perform
EnqueueResolveInAgentJob (waiterRecord.[[AgentSignifier]], waiterRecord.[[PromiseCapability]], waiterRecord.[[Result]]).
- Perform
- Return
unused .
25.4.3.13 EnqueueResolveInAgentJob ( agentSignifier, promiseCapability, resolution )
The abstract operation EnqueueResolveInAgentJob takes arguments agentSignifier (an
- Let resolveJob be a new
Job Abstract Closure with no parameters that captures agentSignifier, promiseCapability, and resolution and performs the following steps when called:Assert :AgentSignifier () is agentSignifier.- Perform !
Call (promiseCapability.[[Resolve]],undefined , « resolution »). - Return
unused .
- Let realmInTargetAgent be !
GetFunctionRealm (promiseCapability.[[Resolve]]). Assert : agentSignifier is realmInTargetAgent.[[AgentSignifier]].- Perform
HostEnqueueGenericJob (resolveJob, realmInTargetAgent). - Return
unused .
25.4.3.14 DoWait ( mode, typedArray, index, value, timeout )
The abstract operation DoWait takes arguments mode (
- Let taRecord be ?
ValidateIntegerTypedArray (typedArray,true ). - Let buffer be taRecord.[[Object]].[[ViewedArrayBuffer]].
- If
IsSharedArrayBuffer (buffer) isfalse , throw aTypeError exception. - Let i be ?
ValidateAtomicAccess (taRecord, index). - Let arrayTypeName be typedArray.[[TypedArrayName]].
- If arrayTypeName is
"BigInt64Array" , let v be ?ToBigInt64 (value). - Else, let v be ?
ToInt32 (value). - Let q be ?
ToNumber (timeout). - If q is either
NaN or+∞ 𝔽, let t be +∞; else if q is-∞ 𝔽, let t be 0; else let t bemax (ℝ (q), 0). - If mode is
sync andAgentCanSuspend () isfalse , throw aTypeError exception. - Let block be buffer.[[ArrayBufferData]].
- Let offset be typedArray.[[ByteOffset]].
- Let byteIndexInBuffer be (i × 4) + offset.
- Let WL be
GetWaiterList (block, byteIndexInBuffer). - If mode is
sync , then- Let promiseCapability be
blocking . - Let resultObject be
undefined .
- Let promiseCapability be
- Else,
- Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let resultObject be
OrdinaryObjectCreate (%Object.prototype% ).
- Let promiseCapability be !
- Perform
EnterCriticalSection (WL). - Let elementType be
TypedArrayElementType (typedArray). - Let w be
GetValueFromBuffer (buffer, byteIndexInBuffer, elementType,true ,seq-cst ). - If v ≠ w, then
- Perform
LeaveCriticalSection (WL). - If mode is
sync , return"not-equal" . - Perform !
CreateDataPropertyOrThrow (resultObject,"async" ,false ). - Perform !
CreateDataPropertyOrThrow (resultObject,"value" ,"not-equal" ). - Return resultObject.
- Perform
- If t = 0 and mode is
async , then- NOTE: There is no special handling of synchronous immediate timeouts. Asynchronous immediate timeouts have special handling in order to fail fast and avoid unnecessary Promise jobs.
- Perform
LeaveCriticalSection (WL). - Perform !
CreateDataPropertyOrThrow (resultObject,"async" ,false ). - Perform !
CreateDataPropertyOrThrow (resultObject,"value" ,"timed-out" ). - Return resultObject.
- Let thisAgent be
AgentSignifier (). - Let now be the
time value (UTC) identifying the current time. - Let additionalTimeout be an
implementation-defined non-negativemathematical value . - Let timeoutTime be
ℝ (now) + t + additionalTimeout. - NOTE: When t is +∞, timeoutTime is also +∞.
- Let waiterRecord be a new
Waiter Record { [[AgentSignifier]]: thisAgent, [[PromiseCapability]]: promiseCapability, [[TimeoutTime]]: timeoutTime, [[Result]]:"ok" }. - Perform
AddWaiter (WL, waiterRecord). - If mode is
sync , then- Perform
SuspendThisAgent (WL, waiterRecord).
- Perform
- Else if timeoutTime is
finite , then- Perform
EnqueueAtomicsWaitAsyncTimeoutJob (WL, waiterRecord).
- Perform
- Perform
LeaveCriticalSection (WL). - If mode is
sync , return waiterRecord.[[Result]]. - Perform !
CreateDataPropertyOrThrow (resultObject,"async" ,true ). - Perform !
CreateDataPropertyOrThrow (resultObject,"value" , promiseCapability.[[Promise]]). - Return resultObject.
additionalTimeout allows implementations to pad timeouts as necessary, such as for reducing power consumption or coarsening timer resolution to mitigate timing attacks. This value may differ from call to call of DoWait.
25.4.3.15 EnqueueAtomicsWaitAsyncTimeoutJob ( WL, waiterRecord )
The abstract operation EnqueueAtomicsWaitAsyncTimeoutJob takes arguments WL (a
- Let timeoutJob be a new
Job Abstract Closure with no parameters that captures WL and waiterRecord and performs the following steps when called:- Perform
EnterCriticalSection (WL). - If WL.[[Waiters]] contains
waiterRecord, then
- Let timeOfJobExecution be the
time value (UTC) identifying the current time. Assert :ℝ (timeOfJobExecution) ≥ waiterRecord.[[TimeoutTime]] (ignoring potential non-monotonicity oftime values ).- Set waiterRecord.[[Result]] to
"timed-out" . - Perform
RemoveWaiter (WL, waiterRecord). - Perform
NotifyWaiter (WL, waiterRecord).
- Let timeOfJobExecution be the
- Perform
LeaveCriticalSection (WL). - Return
unused .
- Perform
- Let now be the
time value (UTC) identifying the current time. - Let currentRealm be
the current Realm Record . - Perform
HostEnqueueTimeoutJob (timeoutJob, currentRealm,𝔽 (waiterRecord.[[TimeoutTime]]) - now). - Return
unused .
25.4.3.16 AtomicCompareExchangeInSharedBlock ( block, byteIndexInBuffer, elementSize, expectedBytes, replacementBytes )
The abstract operation AtomicCompareExchangeInSharedBlock takes arguments block (a
- Let execution be the [[CandidateExecution]]
field of the
surrounding agent 'sAgent Record . - Let eventsRecord be the
Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] isAgentSignifier (). - Let rawBytesRead be a
List of length elementSize whose elements are nondeterministically chosenbyte values . - NOTE: In implementations, rawBytesRead is the result of a load-link, of a
load-exclusive, or of an operand of a read-modify-write instruction on the
underlying hardware. The nondeterminism is a semantic prescription of the
memory model to describe observable behaviour of hardware with weak consistency. - NOTE: The comparison of the expected value and the read value is performed outside
of the
read-modify-write modification function to avoid needlessly strong synchronization when the expected value is not equal to the read value. - If
ByteListEqual (rawBytesRead, expectedBytes) istrue , then- Let second be a new
read-modify-write modification function with parameters (oldBytes, newBytes) that captures nothing and performs the following steps atomically when called:- Return newBytes.
- Let event be
ReadModifyWriteSharedMemory { [[Order]]:seq-cst , [[NoTear]]:true , [[Block]]: block, [[ByteIndex]]: byteIndexInBuffer, [[ElementSize]]: elementSize, [[Payload]]: replacementBytes, [[ModifyOp]]: second }.
- Let second be a new
- Else,
- Let event be
ReadSharedMemory { [[Order]]:seq-cst , [[NoTear]]:true , [[Block]]: block, [[ByteIndex]]: byteIndexInBuffer, [[ElementSize]]: elementSize }.
- Let event be
- Append event to eventsRecord.[[EventList]].
- Append
Chosen Value Record { [[Event]]: event, [[ChosenValue]]: rawBytesRead } to execution.[[ChosenValues]]. - Return rawBytesRead.
25.4.3.17 AtomicReadModifyWrite ( typedArray, index, value, op )
The abstract operation AtomicReadModifyWrite takes arguments typedArray (an
- Let byteIndexInBuffer be ?
ValidateAtomicAccessOnIntegerTypedArray (typedArray, index). - If typedArray.[[ContentType]] is
bigint , let v be ?ToBigInt (value). - Otherwise, let v be
𝔽 (?ToIntegerOrInfinity (value)). - Perform ?
RevalidateAtomicAccess (typedArray, byteIndexInBuffer). - Let buffer be typedArray.[[ViewedArrayBuffer]].
- Let elementType be
TypedArrayElementType (typedArray). - Return
GetModifySetValueInBuffer (buffer, byteIndexInBuffer, elementType, v, op).
25.4.3.18 ByteListBitwiseOp ( op, xBytes, yBytes )
The abstract operation ByteListBitwiseOp takes arguments op (&,
^, or |), xBytes (a
Assert : xBytes and yBytes have the same number of elements.- Let result be a new empty
List . - Let i be 0.
- For each element xByte of xBytes, do
- Let yByte be yBytes[i].
- If op is
&, then- Let resultByte be the result of applying the bitwise AND operation to xByte and yByte.
- Else if op is
^, then- Let resultByte be the result of applying the bitwise exclusive OR (XOR) operation to xByte and yByte.
- Else,
Assert : op is|.- Let resultByte be the result of applying the bitwise inclusive OR operation to xByte and yByte.
- Set i to i + 1.
- Append resultByte to result.
- Return result.
25.4.3.19 ByteListEqual ( xBytes, yBytes )
The abstract operation ByteListEqual takes arguments xBytes (a
- If xBytes and yBytes do not have the same number of elements,
return
false . - Let i be 0.
- For each element xByte of xBytes, do
- Let yByte be yBytes[i].
- If xByte ≠ yByte, return
false . - Set i to i + 1.
- Return
true .
25.4.4 Atomics.add ( typedArray, index, value )
This function performs the following steps when called:
- Let add be a new
read-modify-write modification function with parameters (xBytes, yBytes) that captures typedArray and performs the following steps atomically when called:- Let type be
TypedArrayElementType (typedArray). - Let isLittleEndian be the value of the [[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Let x be
RawBytesToNumeric (type, xBytes, isLittleEndian). - Let y be
RawBytesToNumeric (type, yBytes, isLittleEndian). - If x
is a Number , then- Let sum be
Number::add (x, y).
- Let sum be
- Else,
Assert : xis a BigInt .- Let sum be
BigInt::add (x, y).
- Let sumBytes be
NumericToRawBytes (type, sum, isLittleEndian). Assert : sumBytes, xBytes, and yBytes have the same number of elements.- Return sumBytes.
- Let type be
- Return ?
AtomicReadModifyWrite (typedArray, index, value, add).
25.4.5 Atomics.and ( typedArray, index, value )
This function performs the following steps when called:
- Let and be a new
read-modify-write modification function with parameters (xBytes, yBytes) that captures nothing and performs the following steps atomically when called:- Return
ByteListBitwiseOp (&, xBytes, yBytes).
- Return
- Return ?
AtomicReadModifyWrite (typedArray, index, value, and).
25.4.6 Atomics.compareExchange ( typedArray, index, expectedValue, replacementValue )
This function performs the following steps when called:
- Let byteIndexInBuffer be ?
ValidateAtomicAccessOnIntegerTypedArray (typedArray, index). - Let buffer be typedArray.[[ViewedArrayBuffer]].
- Let block be buffer.[[ArrayBufferData]].
- If typedArray.[[ContentType]] is
bigint , then - Else,
- Let expected be
𝔽 (?ToIntegerOrInfinity (expectedValue)). - Let replacement be
𝔽 (?ToIntegerOrInfinity (replacementValue)).
- Let expected be
- Perform ?
RevalidateAtomicAccess (typedArray, byteIndexInBuffer). - Let elementType be
TypedArrayElementType (typedArray). - Let elementSize be
TypedArrayElementSize (typedArray). - Let isLittleEndian be the value of the [[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Let expectedBytes be
NumericToRawBytes (elementType, expected, isLittleEndian). - Let replacementBytes be
NumericToRawBytes (elementType, replacement, isLittleEndian). - If
IsSharedArrayBuffer (buffer) istrue , then- Let rawBytesRead be
AtomicCompareExchangeInSharedBlock (block, byteIndexInBuffer, elementSize, expectedBytes, replacementBytes).
- Let rawBytesRead be
- Else,
- Let rawBytesRead be a
List of length elementSize whose elements are the sequence of elementSize bytes starting with block[byteIndexInBuffer]. - If
ByteListEqual (rawBytesRead, expectedBytes) istrue , then- Store the individual bytes of replacementBytes into block, starting at block[byteIndexInBuffer].
- Let rawBytesRead be a
- Return
RawBytesToNumeric (elementType, rawBytesRead, isLittleEndian).
25.4.7 Atomics.exchange ( typedArray, index, value )
This function performs the following steps when called:
- Let second be a new
read-modify-write modification function with parameters (oldBytes, newBytes) that captures nothing and performs the following steps atomically when called:- Return newBytes.
- Return ?
AtomicReadModifyWrite (typedArray, index, value, second).
25.4.8 Atomics.isLockFree ( size )
This function performs the following steps when called:
- Let n be ?
ToIntegerOrInfinity (size). - Let AR be the
Agent Record of thesurrounding agent . - If n = 1, return AR.[[IsLockFree1]].
- If n = 2, return AR.[[IsLockFree2]].
- If n = 4, return
true . - If n = 8, return AR.[[IsLockFree8]].
- Return
false .
This function is an optimization primitive. The intuition is that if the atomic step of
an atomic primitive (compareExchange, load,
store, add, sub, and,
or, xor, or exchange) on a datum of size
n bytes will be performed without the Atomics.isLockFree(n) will return
Atomics.isLockFree(4) always returns
Regardless of the value returned by this function, all atomic operations are guaranteed to be atomic. For example, they will never have a visible operation take place in the middle of the operation (e.g., "tearing").
25.4.9 Atomics.load ( typedArray, index )
This function performs the following steps when called:
- Let byteIndexInBuffer be ?
ValidateAtomicAccessOnIntegerTypedArray (typedArray, index). - Perform ?
RevalidateAtomicAccess (typedArray, byteIndexInBuffer). - Let buffer be typedArray.[[ViewedArrayBuffer]].
- Let elementType be
TypedArrayElementType (typedArray). - Return
GetValueFromBuffer (buffer, byteIndexInBuffer, elementType,true ,seq-cst ).
25.4.10 Atomics.or ( typedArray, index, value )
This function performs the following steps when called:
- Let or be a new
read-modify-write modification function with parameters (xBytes, yBytes) that captures nothing and performs the following steps atomically when called:- Return
ByteListBitwiseOp (|, xBytes, yBytes).
- Return
- Return ?
AtomicReadModifyWrite (typedArray, index, value, or).
25.4.11 Atomics.store ( typedArray, index, value )
This function performs the following steps when called:
- Let byteIndexInBuffer be ?
ValidateAtomicAccessOnIntegerTypedArray (typedArray, index). - If typedArray.[[ContentType]] is
bigint , let v be ?ToBigInt (value). - Otherwise, let v be
𝔽 (?ToIntegerOrInfinity (value)). - Perform ?
RevalidateAtomicAccess (typedArray, byteIndexInBuffer). - Let buffer be typedArray.[[ViewedArrayBuffer]].
- Let elementType be
TypedArrayElementType (typedArray). - Perform
SetValueInBuffer (buffer, byteIndexInBuffer, elementType, v,true ,seq-cst ). - Return v.
25.4.12 Atomics.sub ( typedArray, index, value )
This function performs the following steps when called:
- Let subtract be a new
read-modify-write modification function with parameters (xBytes, yBytes) that captures typedArray and performs the following steps atomically when called:- Let type be
TypedArrayElementType (typedArray). - Let isLittleEndian be the value of the [[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Let x be
RawBytesToNumeric (type, xBytes, isLittleEndian). - Let y be
RawBytesToNumeric (type, yBytes, isLittleEndian). - If x
is a Number , then- Let difference be
Number::subtract (x, y).
- Let difference be
- Else,
Assert : xis a BigInt .- Let difference be
BigInt::subtract (x, y).
- Let differenceBytes be
NumericToRawBytes (type, difference, isLittleEndian). Assert : differenceBytes, xBytes, and yBytes have the same number of elements.- Return differenceBytes.
- Let type be
- Return ?
AtomicReadModifyWrite (typedArray, index, value, subtract).
25.4.13 Atomics.wait ( typedArray, index, value, timeout )
This function puts the
It performs the following steps when called:
- Return ?
DoWait (sync , typedArray, index, value, timeout).
25.4.14 Atomics.waitAsync ( typedArray, index, value, timeout )
This function returns a Promise that is resolved when the calling
It performs the following steps when called:
- Return ?
DoWait (async , typedArray, index, value, timeout).
25.4.15 Atomics.notify ( typedArray, index, count )
This function notifies some
It performs the following steps when called:
- Let taRecord be ?
ValidateIntegerTypedArray (typedArray,true ). - Let byteIndexInBuffer be ?
ValidateAtomicAccess (taRecord, index). - If count is
undefined , then- Let c be +∞.
- Else,
- Let intCount be ?
ToIntegerOrInfinity (count). - Let c be
max (intCount, 0).
- Let intCount be ?
- Let buffer be typedArray.[[ViewedArrayBuffer]].
- Let block be buffer.[[ArrayBufferData]].
- If
IsSharedArrayBuffer (buffer) isfalse , return+0 𝔽. - Let WL be
GetWaiterList (block, byteIndexInBuffer). - Perform
EnterCriticalSection (WL). - Let S be
RemoveWaiters (WL, c). - For each element W of S, do
- Perform
NotifyWaiter (WL, W).
- Perform
- Perform
LeaveCriticalSection (WL). - Let n be the number of elements in S.
- Return
𝔽 (n).
25.4.16 Atomics.xor ( typedArray, index, value )
This function performs the following steps when called:
- Let xor be a new
read-modify-write modification function with parameters (xBytes, yBytes) that captures nothing and performs the following steps atomically when called:- Return
ByteListBitwiseOp (^, xBytes, yBytes).
- Return
- Return ?
AtomicReadModifyWrite (typedArray, index, value, xor).
25.4.17 Atomics [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
25.5 The JSON Object
The JSON object:
- is %JSON%.
- is the initial value of the
"JSON" property of theglobal object . - is an
ordinary object . - contains two functions,
parseandstringify, that are used to parse and construct JSON texts. - has a [[Prototype]] internal slot whose value is
%Object.prototype% . - does not have a [[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a [[Call]] internal method; it cannot be invoked as a function.
The JSON Data Interchange Format is defined in ECMA-404. The JSON interchange format used in this
specification is exactly that described by ECMA-404. Conforming implementations of
JSON.parse and JSON.stringify must support the exact interchange format
described in the ECMA-404 specification without any deletions or extensions to the format.
25.5.1 JSON.parse ( text [ , reviver ] )
This function parses a JSON text (a JSON-formatted String) and produces an
The optional reviver parameter is a function that takes two parameters, key
and value. It can filter and transform the results. It is called with each of the
key/value pairs produced by the parse, and its return value is used
instead of the original value. If it returns what it received, the structure is not modified. If
it returns
- Let jsonString be ?
ToString (text). - Let unfiltered be ?
ParseJSON (jsonString). - If
IsCallable (reviver) istrue , then- Let root be
OrdinaryObjectCreate (%Object.prototype% ). - Let rootName be the empty String.
- Perform !
CreateDataPropertyOrThrow (root, rootName, unfiltered). - Return ?
InternalizeJSONProperty (root, rootName, reviver).
- Let root be
- Else,
- Return unfiltered.
The
25.5.1.1 ParseJSON ( text )
The abstract operation ParseJSON takes argument text (a String) and returns either
a
- If
StringToCodePoints (text) is not a valid JSON text as specified in ECMA-404, throw aSyntaxError exception. - Let scriptString be the
string-concatenation of"(" , text, and");" . - Let script be
ParseText (scriptString,Script ). - NOTE: The
early error rules defined in13.2.5.1 have special handling for the above invocation ofParseText . Assert : script is aParse Node .- Let result be !
Evaluation of script. - NOTE: The
PropertyDefinitionEvaluation semantics defined in13.2.5.5 have special handling for the above evaluation. Assert : result is either a String, a Number, a Boolean, an Object that is defined by either anArrayLiteral or anObjectLiteral , ornull .- Return result.
It is not permitted for a conforming implementation of JSON.parse to extend the
JSON grammars. If an implementation wishes to support a modified or extended JSON
interchange format it must do so by defining a different parse function.
Valid JSON text is a subset of the ECMAScript
However, because
In the case where there are duplicate name Strings within an object, lexically preceding values for the same key shall be overwritten.
25.5.1.2 InternalizeJSONProperty ( holder, name, reviver )
The abstract operation InternalizeJSONProperty takes arguments holder (an Object),
name (a String), and reviver (a
This algorithm intentionally does not throw an exception if either [[Delete]] or
It performs the following steps when called:
- Let val be ?
Get (holder, name). - If val
is an Object , then- Let isArray be ?
IsArray (val). - If isArray is
true , then- Let len be ?
LengthOfArrayLike (val). - Let I be 0.
- Repeat, while I < len,
- Let prop be !
ToString (𝔽 (I)). - Let newElement be ?
InternalizeJSONProperty (val, prop, reviver). - If newElement is
undefined , then- Perform ? val.[[Delete]](prop).
- Else,
- Perform ?
CreateDataProperty (val, prop, newElement).
- Perform ?
- Set I to I + 1.
- Let prop be !
- Let len be ?
- Else,
- Let keys be ?
EnumerableOwnProperties (val,key ). - For each String P of keys, do
- Let newElement be ?
InternalizeJSONProperty (val, P, reviver). - If newElement is
undefined , then- Perform ? val.[[Delete]](P).
- Else,
- Perform ?
CreateDataProperty (val, P, newElement).
- Perform ?
- Let newElement be ?
- Let keys be ?
- Let isArray be ?
- Return ?
Call (reviver, holder, « name, val »).
25.5.2 JSON.stringify ( value [ , replacer [ , space ] ] )
This function returns a String in UTF-16 encoded JSON format representing an
It performs the following steps when called:
- Let stack be a new empty
List . - Let indent be the empty String.
- Let PropertyList be
undefined . - Let ReplacerFunction be
undefined . - If replacer
is an Object , then- If
IsCallable (replacer) istrue , then- Set ReplacerFunction to replacer.
- Else,
- Let isArray be ?
IsArray (replacer). - If isArray is
true , then- Set PropertyList to a new empty
List . - Let len be ?
LengthOfArrayLike (replacer). - Let k be 0.
- Repeat, while k < len,
- Let prop be !
ToString (𝔽 (k)). - Let v be ?
Get (replacer, prop). - Let item be
undefined . - If v
is a String , then- Set item to v.
- Else if v
is a Number , then- Set item to !
ToString (v).
- Set item to !
- Else if v
is an Object , then- If v has a [[StringData]] or [[NumberData]] internal
slot, set item to ?
ToString (v).
- If v has a [[StringData]] or [[NumberData]] internal
slot, set item to ?
- If item is not
undefined and PropertyList does not contain item, then- Append item to PropertyList.
- Set k to k + 1.
- Let prop be !
- Set PropertyList to a new empty
- Let isArray be ?
- If
- If space
is an Object , then - If space
is a Number , then- Let spaceMV be !
ToIntegerOrInfinity (space). - Set spaceMV to
min (10, spaceMV). - If spaceMV < 1, let gap be the empty String; otherwise let gap be the String value containing spaceMV occurrences of the code unit 0x0020 (SPACE).
- Let spaceMV be !
- Else if space
is a String , then- If the length of space ≤ 10, let gap be space;
otherwise let gap be the
substring of space from 0 to 10.
- If the length of space ≤ 10, let gap be space;
otherwise let gap be the
- Else,
- Let gap be the empty String.
- Let wrapper be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (wrapper, the empty String, value). - Let state be the
JSON Serialization Record { [[ReplacerFunction]]: ReplacerFunction, [[Stack]]: stack, [[Indent]]: indent, [[Gap]]: gap, [[PropertyList]]: PropertyList }. - Return ?
SerializeJSONProperty (state, the empty String, wrapper).
The
JSON structures are allowed to be nested to any depth, but they must be acyclic. If
value is or contains a cyclic structure, then this function must throw a
a = [];
a[0] = a;
my_text = JSON.stringify(a); // This must throw a TypeError.Symbolic primitive values are rendered as follows:
-
The
null value is rendered in JSON text as the String value"null" . -
The
undefined value is not rendered. -
The
true value is rendered in JSON text as the String value"true" . -
The
false value is rendered in JSON text as the String value"false" .
String values are wrapped in QUOTATION MARK (") code units. The code units
" and \ are escaped with \ prefixes. Control
characters code units are replaced with escape sequences \uHHHH, or with
the shorter forms, \b (BACKSPACE), \f (FORM FEED),
\n (LINE FEED), \r (CARRIAGE RETURN), \t
(CHARACTER TABULATION).
Values that do not have a JSON representation (such as
An object is rendered as U+007B (LEFT CURLY BRACKET) followed by zero or more properties,
separated with a U+002C (COMMA), closed with a U+007D (RIGHT CURLY BRACKET). A property
is a quoted String representing the
25.5.2.1 JSON Serialization Record
A JSON Serialization Record is
a
JSON Serialization Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[ReplacerFunction]] | a |
A function that can supply replacement values for object properties (from JSON.stringify's replacer parameter). |
| [[PropertyList]] | either a |
The names of properties to include when serializing a non-array object (from JSON.stringify's replacer parameter). |
| [[Gap]] | a String | The unit of indentation (from JSON.stringify's space parameter). |
| [[Stack]] | a |
The set of nested objects that are in the process of being serialized. Used to detect cyclic structures. |
| [[Indent]] | a String | The current indentation. |
25.5.2.2 SerializeJSONProperty ( state, key, holder )
The abstract operation SerializeJSONProperty takes arguments state (a
- Let value be ?
Get (holder, key). - If value
is an Object or valueis a BigInt , then- Let toJSON be ?
GetV (value,"toJSON" ). - If
IsCallable (toJSON) istrue , then- Set value to ?
Call (toJSON, value, « key »).
- Set value to ?
- Let toJSON be ?
- If state.[[ReplacerFunction]] is not
undefined , then- Set value to ?
Call (state.[[ReplacerFunction]], holder, « key, value »).
- Set value to ?
- If value
is an Object , then- If value has a [[NumberData]] internal
slot, then
- Set value to ?
ToNumber (value).
- Set value to ?
- Else if value has a [[StringData]]
internal slot, then
- Set value to ?
ToString (value).
- Set value to ?
- Else if value has a [[BooleanData]]
internal slot, then
- Set value to value.[[BooleanData]].
- Else if value has a [[BigIntData]]
internal slot, then
- Set value to value.[[BigIntData]].
- If value has a [[NumberData]] internal
slot, then
- If value is
null , return"null" . - If value is
true , return"true" . - If value is
false , return"false" . - If value
is a String , returnQuoteJSONString (value). - If value
is a Number , then - If value
is a BigInt , throw aTypeError exception. - If value
is an Object andIsCallable (value) isfalse , then- Let isArray be ?
IsArray (value). - If isArray is
true , return ?SerializeJSONArray (state, value). - Return ?
SerializeJSONObject (state, value).
- Let isArray be ?
- Return
undefined .
25.5.2.3 QuoteJSONString ( value )
The abstract operation QuoteJSONString takes argument value (a String) and returns
a String. It wraps value in 0x0022 (QUOTATION MARK) code units and escapes
certain other code units within it. This operation interprets value as a sequence
of UTF-16 encoded code points, as described in
- Let product be the String value consisting solely of the code unit 0x0022 (QUOTATION MARK).
- For each code point C of
StringToCodePoints (value), do- If C is listed in the “Code Point” column of
Table 81 , then- Set product to the
string-concatenation of product and the escape sequence for C as specified in the “Escape Sequence” column of the corresponding row.
- Set product to the
- Else if C has a numeric value less than 0x0020 (SPACE) or
C has the same numeric value as a
leading surrogate ortrailing surrogate , then- Let unit be the code unit whose numeric value is the numeric value of C.
- Set product to the
string-concatenation of product andUnicodeEscape (unit).
- Else,
- Set product to the
string-concatenation of product andUTF16EncodeCodePoint (C).
- Set product to the
- If C is listed in the “Code Point” column of
- Set product to the
string-concatenation of product and the code unit 0x0022 (QUOTATION MARK). - Return product.
| Code Point | Unicode Character Name | Escape Sequence |
|---|---|---|
| U+0008 | BACKSPACE |
\b
|
| U+0009 | CHARACTER TABULATION |
\t
|
| U+000A | LINE FEED (LF) |
\n
|
| U+000C | FORM FEED (FF) |
\f
|
| U+000D | CARRIAGE RETURN (CR) |
\r
|
| U+0022 | QUOTATION MARK |
\"
|
| U+005C | REVERSE SOLIDUS |
\\
|
25.5.2.4 UnicodeEscape ( C )
The abstract operation UnicodeEscape takes argument C (a code unit) and returns a String. It represents C as a Unicode escape sequence. It performs the following steps when called:
- Let n be the numeric value of C.
Assert : n ≤ 0xFFFF.- Let hex be the String representation of n, formatted as a lowercase hexadecimal number.
- Return the
string-concatenation of the code unit 0x005C (REVERSE SOLIDUS),"u" , andStringPad (hex, 4,"0" ,start ).
25.5.2.5 SerializeJSONObject ( state, value )
The abstract operation SerializeJSONObject takes arguments state (a
- If state.[[Stack]] contains value,
throw a
TypeError exception because the structure is cyclical. - Append value to state.[[Stack]].
- Let stepBack be state.[[Indent]].
- Set state.[[Indent]] to the
string-concatenation of state.[[Indent]] and state.[[Gap]]. - If state.[[PropertyList]] is not
undefined , then- Let K be state.[[PropertyList]].
- Else,
- Let K be ?
EnumerableOwnProperties (value,key ).
- Let K be ?
- Let partial be a new empty
List . - For each element P of K, do
- Let strP be ?
SerializeJSONProperty (state, P, value). - If strP is not
undefined , then- Let member be
QuoteJSONString (P). - Set member to the
string-concatenation of member and":" . - If state.[[Gap]] is not the
empty String, then
- Set member to the
string-concatenation of member and the code unit 0x0020 (SPACE).
- Set member to the
- Set member to the
string-concatenation of member and strP. - Append member to partial.
- Let member be
- Let strP be ?
- If partial is empty, then
- Let final be
"{}" .
- Let final be
- Else,
- If state.[[Gap]] is the empty String,
then
- Let properties be the String value formed by concatenating all the element Strings of partial with each adjacent pair of Strings separated with the code unit 0x002C (COMMA). A comma is not inserted either before the first String or after the last String.
- Let final be the
string-concatenation of"{" , properties, and"}" .
- Else,
- Let separator be the
string-concatenation of the code unit 0x002C (COMMA), the code unit 0x000A (LINE FEED), and state.[[Indent]]. - Let properties be the String value formed by concatenating all the element Strings of partial with each adjacent pair of Strings separated with separator. The separator String is not inserted either before the first String or after the last String.
- Let final be the
string-concatenation of"{" , the code unit 0x000A (LINE FEED), state.[[Indent]], properties, the code unit 0x000A (LINE FEED), stepBack, and"}" .
- Let separator be the
- If state.[[Gap]] is the empty String,
then
- Remove the last element of state.[[Stack]].
- Set state.[[Indent]] to stepBack.
- Return final.
25.5.2.6 SerializeJSONArray ( state, value )
The abstract operation SerializeJSONArray takes arguments state (a
- If state.[[Stack]] contains value,
throw a
TypeError exception because the structure is cyclical. - Append value to state.[[Stack]].
- Let stepBack be state.[[Indent]].
- Set state.[[Indent]] to the
string-concatenation of state.[[Indent]] and state.[[Gap]]. - Let partial be a new empty
List . - Let len be ?
LengthOfArrayLike (value). - Let index be 0.
- Repeat, while index < len,
- Let strP be ?
SerializeJSONProperty (state, !ToString (𝔽 (index)), value). - If strP is
undefined , then- Append
"null" to partial.
- Append
- Else,
- Append strP to partial.
- Set index to index + 1.
- Let strP be ?
- If partial is empty, then
- Let final be
"[]" .
- Let final be
- Else,
- If state.[[Gap]] is the empty String,
then
- Let properties be the String value formed by concatenating all the element Strings of partial with each adjacent pair of Strings separated with the code unit 0x002C (COMMA). A comma is not inserted either before the first String or after the last String.
- Let final be the
string-concatenation of"[" , properties, and"]" .
- Else,
- Let separator be the
string-concatenation of the code unit 0x002C (COMMA), the code unit 0x000A (LINE FEED), and state.[[Indent]]. - Let properties be the String value formed by concatenating all the element Strings of partial with each adjacent pair of Strings separated with separator. The separator String is not inserted either before the first String or after the last String.
- Let final be the
string-concatenation of"[" , the code unit 0x000A (LINE FEED), state.[[Indent]], properties, the code unit 0x000A (LINE FEED), stepBack, and"]" .
- Let separator be the
- If state.[[Gap]] is the empty String,
then
- Remove the last element of state.[[Stack]].
- Set state.[[Indent]] to stepBack.
- Return final.
The representation of arrays includes only the elements in the array.length
(exclusive). Properties whose keys are not
25.5.3 JSON [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
26 Managing Memory
26.1 WeakRef Objects
A
26.1.1 The WeakRef Constructor
The WeakRef
- is %WeakRef%.
-
is the initial value of the
"WeakRef" property of theglobal object . -
creates and initializes a new WeakRef when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
-
may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specifiedWeakRefbehaviour must include asupercall to theWeakRefconstructor to create and initialize the subclass instance with the internal state necessary to support theWeakRef.prototypebuilt-in methods.
26.1.1.1 WeakRef ( target )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - If
CanBeHeldWeakly (target) isfalse , throw aTypeError exception. - Let weakRef be ?
OrdinaryCreateFromConstructor (NewTarget,"%WeakRef.prototype%" , « [[WeakRefTarget]] »). - Perform
AddToKeptObjects (target). - Set weakRef.[[WeakRefTarget]] to target.
- Return weakRef.
26.1.2 Properties of the WeakRef Constructor
The
-
has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
26.1.2.1 WeakRef.prototype
The initial value of WeakRef.prototype is the
This property has the attributes { [[Writable]]:
26.1.3 Properties of the WeakRef Prototype Object
The WeakRef prototype object:
- is %WeakRef.prototype%.
-
has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a [[WeakRefTarget]] internal slot.
26.1.3.1 WeakRef.prototype.constructor
The initial value of WeakRef.prototype.constructor is
26.1.3.2 WeakRef.prototype.deref ( )
This method performs the following steps when called:
- Let weakRef be the
this value. - Perform ?
RequireInternalSlot (weakRef, [[WeakRefTarget]]). - Return
WeakRefDeref (weakRef).
If the
let target = { foo() {} };
let weakRef = new WeakRef(target);
// ... later ...
if (weakRef.deref()) {
weakRef.deref().foo();
}In the above example, if the first deref does not evaluate to
26.1.3.3 WeakRef.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
26.1.4 WeakRef Abstract Operations
26.1.4.1 WeakRefDeref ( weakRef )
The abstract operation WeakRefDeref takes argument weakRef (a
- Let target be weakRef.[[WeakRefTarget]].
- If target is not
empty , then- Perform
AddToKeptObjects (target). - Return target.
- Perform
- Return
undefined .
This abstract operation is defined separately from WeakRef.prototype.deref strictly to make it possible to succinctly define liveness.
26.1.5 Properties of WeakRef Instances
26.2 FinalizationRegistry Objects
A
26.2.1 The FinalizationRegistry Constructor
The FinalizationRegistry
- is %FinalizationRegistry%.
-
is the initial value of the
"FinalizationRegistry" property of theglobal object . -
creates and initializes a new FinalizationRegistry when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
-
may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specifiedFinalizationRegistrybehaviour must include asupercall to theFinalizationRegistryconstructor to create and initialize the subclass instance with the internal state necessary to support theFinalizationRegistry.prototypebuilt-in methods.
26.2.1.1 FinalizationRegistry ( cleanupCallback )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - If
IsCallable (cleanupCallback) isfalse , throw aTypeError exception. - Let finalizationRegistry be ?
OrdinaryCreateFromConstructor (NewTarget,"%FinalizationRegistry.prototype%" , « [[Realm]], [[CleanupCallback]], [[Cells]] »). - Let fn be the
active function object . - Set finalizationRegistry.[[Realm]] to fn.[[Realm]].
- Set finalizationRegistry.[[CleanupCallback]] to
HostMakeJobCallback (cleanupCallback). - Set finalizationRegistry.[[Cells]] to a new
empty
List . - Return finalizationRegistry.
26.2.2 Properties of the FinalizationRegistry Constructor
The
-
has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
26.2.2.1 FinalizationRegistry.prototype
The initial value of FinalizationRegistry.prototype is the
This property has the attributes { [[Writable]]:
26.2.3 Properties of the FinalizationRegistry Prototype Object
The FinalizationRegistry prototype object:
- is %FinalizationRegistry.prototype%.
-
has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have [[Cells]] and [[CleanupCallback]] internal slots.
26.2.3.1 FinalizationRegistry.prototype.constructor
The initial value of FinalizationRegistry.prototype.constructor is
26.2.3.2 FinalizationRegistry.prototype.register ( target, heldValue [ , unregisterToken ] )
This method performs the following steps when called:
- Let finalizationRegistry be the
this value. - Perform ?
RequireInternalSlot (finalizationRegistry, [[Cells]]). - If
CanBeHeldWeakly (target) isfalse , throw aTypeError exception. - If
SameValue (target, heldValue) istrue , throw aTypeError exception. - If
CanBeHeldWeakly (unregisterToken) isfalse , then- If unregisterToken is not
undefined , throw aTypeError exception. - Set unregisterToken to
empty .
- If unregisterToken is not
- Let cell be the
Record { [[WeakRefTarget]]: target, [[HeldValue]]: heldValue, [[UnregisterToken]]: unregisterToken }. - Append cell to finalizationRegistry.[[Cells]].
- Return
undefined .
Based on the algorithms and definitions in this specification, cell.[[HeldValue]] is
26.2.3.3 FinalizationRegistry.prototype.unregister ( unregisterToken )
This method performs the following steps when called:
- Let finalizationRegistry be the
this value. - Perform ?
RequireInternalSlot (finalizationRegistry, [[Cells]]). - If
CanBeHeldWeakly (unregisterToken) isfalse , throw aTypeError exception. - Let removed be
false . - For each
Record { [[WeakRefTarget]], [[HeldValue]], [[UnregisterToken]] } cell of finalizationRegistry.[[Cells]], do- If cell.[[UnregisterToken]] is not
empty andSameValue (cell.[[UnregisterToken]], unregisterToken) istrue , then- Remove cell from finalizationRegistry.[[Cells]].
- Set removed to
true .
- If cell.[[UnregisterToken]] is not
- Return removed.
26.2.3.4 FinalizationRegistry.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
26.2.4 Properties of FinalizationRegistry Instances
27 Control Abstraction Objects
27.1 Iteration
27.1.1 Common Iteration Interfaces
An interface is a set of
27.1.1.1 The Iterable Interface
The iterable interface includes the property described in
| Property | Value | Requirements |
|---|---|---|
%Symbol.iterator%
|
a function that returns an |
The returned object must conform to the |
27.1.1.2 The Iterator Interface
An object that implements the iterator
interface must include the property in
| Property | Value | Requirements |
|---|---|---|
|
|
a function that returns an |
The returned object must conform to the next method of an next method of that object should also return an |
Arguments may be passed to the next function but their interpretation
and validity is dependent upon the target iterator. The for-of statement and other
common users of iterators do not pass any arguments, so iterator objects that expect
to be used in such a manner must be prepared to deal with being called with no
arguments.
| Property | Value | Requirements |
|---|---|---|
|
|
a function that returns an |
The returned object must conform to the next
method calls to the return method.
However, this requirement is not enforced.
|
|
|
a function that returns an |
The returned object must conform to the throw the value passed as
the argument. If the method does not throw, the returned
|
Typically callers of these methods should check for their existence before invoking
them. Certain ECMAScript language features including
for-of, yield*, and array destructuring call
these methods after performing an existence check. Most ECMAScript library functions
that accept
27.1.1.3 The Async Iterable Interface
The async iterable interface includes the properties described in
| Property | Value | Requirements |
|---|---|---|
%Symbol.asyncIterator% |
a function that returns an |
The returned object must conform to the |
27.1.1.4 The Async Iterator Interface
An object that implements the async iterator interface must include the properties in
| Property | Value | Requirements |
|---|---|---|
| a function that returns a promise for an |
The returned promise, when fulfilled, must fulfill with an object
that conforms to the Additionally, the |
Arguments may be passed to the next function but their interpretation
and validity is dependent upon the target async iterator. The
for-await-of statement and other common users
of async iterators do not pass any arguments, so async iterator objects that expect
to be used in such a manner must be prepared to deal with being called with no
arguments.
| Property | Value | Requirements |
|---|---|---|
| a function that returns a promise for an |
The returned promise, when fulfilled, must fulfill with an object
that conforms to the Additionally, the |
|
| a function that returns a promise for an |
The returned promise, when fulfilled, must fulfill with an object
that conforms to the If the returned promise is fulfilled, the |
Typically callers of these methods should check for their existence before invoking
them. Certain ECMAScript language features including
for-await-of and yield* call
these methods after performing an existence check.
27.1.1.5 The IteratorResult Interface
The IteratorResult
interface includes the properties listed in
| Property | Value | Requirements |
|---|---|---|
|
|
a Boolean |
This is the result status of an next method call. If the end of the |
|
|
an |
If done is |
27.1.2 Iterator Helper Objects
An Iterator Helper object is an
27.1.2.1 The %IteratorHelperPrototype% Object
The %IteratorHelperPrototype% object:
- has properties that are inherited by all
Iterator Helper objects . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Iterator.prototype% . - has the following properties:
27.1.2.1.1 %IteratorHelperPrototype%.next ( )
- Return ?
GeneratorResume (this value,undefined ,"Iterator Helper" ).
27.1.2.1.2 %IteratorHelperPrototype%.return ( )
- Let O be
this value. - Perform ?
RequireInternalSlot (O, [[UnderlyingIterator]]). Assert : O has a [[GeneratorState]] internal slot.- If O.[[GeneratorState]] is
suspended-start , then- Set O.[[GeneratorState]] to
completed . - NOTE: Once a generator enters the completed state it never leaves it and
its associated
execution context is never resumed. Any execution state associated with O can be discarded at this point. - Perform ?
IteratorClose (O.[[UnderlyingIterator]],NormalCompletion (unused )). - Return
CreateIteratorResultObject (undefined ,true ).
- Set O.[[GeneratorState]] to
- Let C be
ReturnCompletion (undefined ). - Return ?
GeneratorResumeAbrupt (O, C,"Iterator Helper" ).
27.1.2.1.3 %IteratorHelperPrototype% [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
27.1.3 Iterator Objects
27.1.3.1 The Iterator Constructor
The Iterator
- is %Iterator%.
- is the initial value of the
"Iterator" property of theglobal object . - is designed to be subclassable. It may be used as the value of an
extends clause of a class definition.
27.1.3.1.1 Iterator ( )
This function performs the following steps when called:
- If NewTarget is either
undefined or theactive function object , throw aTypeError exception. - Return ?
OrdinaryCreateFromConstructor (NewTarget,"%Iterator.prototype%" ).
27.1.3.2 Properties of the Iterator Constructor
The
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
27.1.3.2.1 Iterator.from ( O )
- Let iteratorRecord be ?
GetIteratorFlattenable (O,iterate-string-primitives ). - Let hasInstance be ?
OrdinaryHasInstance (%Iterator% , iteratorRecord.[[Iterator]]). - If hasInstance is
true , then- Return iteratorRecord.[[Iterator]].
- Let wrapper be
OrdinaryObjectCreate (%WrapForValidIteratorPrototype% , « [[Iterated]] »). - Set wrapper.[[Iterated]] to iteratorRecord.
- Return wrapper.
27.1.3.2.1.1 The %WrapForValidIteratorPrototype% Object
The %WrapForValidIteratorPrototype% object:
- is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Iterator.prototype% .
27.1.3.2.1.1.1 %WrapForValidIteratorPrototype%.next ( )
- Let O be
this value. - Perform ?
RequireInternalSlot (O, [[Iterated]]). - Let iteratorRecord be O.[[Iterated]].
- Return ?
Call (iteratorRecord.[[NextMethod]], iteratorRecord.[[Iterator]]).
27.1.3.2.1.1.2 %WrapForValidIteratorPrototype%.return ( )
- Let O be
this value. - Perform ?
RequireInternalSlot (O, [[Iterated]]). - Let iterator be O.[[Iterated]].[[Iterator]].
Assert : iteratoris an Object .- Let returnMethod be ?
GetMethod (iterator,"return" ). - If returnMethod is
undefined , then- Return
CreateIteratorResultObject (undefined ,true ).
- Return
- Return ?
Call (returnMethod, iterator).
27.1.3.2.2 Iterator.prototype
The initial value of Iterator.prototype is the
This property has the attributes { [[Writable]]:
27.1.4 Properties of the Iterator Prototype Object
The Iterator prototype object:
- is %Iterator.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object .
All objects defined in this specification that implement the
The following expression is one way that ECMAScript code can access the %Iterator.prototype% object:
Object.getPrototypeOf(Object.getPrototypeOf([][Symbol.iterator]()))27.1.4.1 Iterator.prototype.constructor
Iterator.prototype.constructor is an
27.1.4.1.1 get Iterator.prototype.constructor
The value of the [[Get]] attribute is a built-in function that requires no arguments. It performs the following steps when called:
- Return
%Iterator% .
27.1.4.1.2 set Iterator.prototype.constructor
The value of the [[Set]] attribute is a built-in function that takes an argument v. It performs the following steps when called:
- Perform ?
SetterThatIgnoresPrototypeProperties (this value,%Iterator.prototype% ,"constructor" , v). - Return
undefined .
Unlike the
27.1.4.2 Iterator.prototype.drop ( limit )
This method performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - Let iterated be the
Iterator Record { [[Iterator]]: O, [[NextMethod]]:undefined , [[Done]]:false }. - Let numLimit be
Completion (ToNumber (limit)). IfAbruptCloseIterator (numLimit, iterated).- If numLimit is
NaN , then- Let error be
ThrowCompletion (a newly createdRangeError object). - Return ?
IteratorClose (iterated, error).
- Let error be
- Let integerLimit be !
ToIntegerOrInfinity (numLimit). - If integerLimit < 0, then
- Let error be
ThrowCompletion (a newly createdRangeError object). - Return ?
IteratorClose (iterated, error).
- Let error be
- Set iterated to ?
GetIteratorDirect (O). - Let closure be a new
Abstract Closure with no parameters that captures iterated and integerLimit and performs the following steps when called:- Let remaining be integerLimit.
- Repeat, while remaining > 0,
- If remaining ≠ +∞, then
- Set remaining to remaining - 1.
- Let next be ?
IteratorStep (iterated). - If next is
done , returnReturnCompletion (undefined ).
- If remaining ≠ +∞, then
- Repeat,
- Let value be ?
IteratorStepValue (iterated). - If value is
done , returnReturnCompletion (undefined ). - Let completion be
Completion (Yield (value)). IfAbruptCloseIterator (completion, iterated).
- Let value be ?
- Let result be
CreateIteratorFromClosure (closure,"Iterator Helper" ,%IteratorHelperPrototype% , « [[UnderlyingIterator]] »). - Set result.[[UnderlyingIterator]] to iterated.
- Return result.
27.1.4.3 Iterator.prototype.every ( predicate )
This method performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - Let iterated be the
Iterator Record { [[Iterator]]: O, [[NextMethod]]:undefined , [[Done]]:false }. - If
IsCallable (predicate) isfalse , then- Let error be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iterated, error).
- Let error be
- Set iterated to ?
GetIteratorDirect (O). - Let counter be 0.
- Repeat,
- Let value be ?
IteratorStepValue (iterated). - If value is
done , returntrue . - Let result be
Completion (Call (predicate,undefined , « value,𝔽 (counter) »)). IfAbruptCloseIterator (result, iterated).- If
ToBoolean (result) isfalse , return ?IteratorClose (iterated,NormalCompletion (false )). - Set counter to counter + 1.
- Let value be ?
27.1.4.4 Iterator.prototype.filter ( predicate )
This method performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - Let iterated be the
Iterator Record { [[Iterator]]: O, [[NextMethod]]:undefined , [[Done]]:false }. - If
IsCallable (predicate) isfalse , then- Let error be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iterated, error).
- Let error be
- Set iterated to ?
GetIteratorDirect (O). - Let closure be a new
Abstract Closure with no parameters that captures iterated and predicate and performs the following steps when called:- Let counter be 0.
- Repeat,
- Let value be ?
IteratorStepValue (iterated). - If value is
done , returnReturnCompletion (undefined ). - Let selected be
Completion (Call (predicate,undefined , « value,𝔽 (counter) »)). IfAbruptCloseIterator (selected, iterated).- If
ToBoolean (selected) istrue , then- Let completion be
Completion (Yield (value)). IfAbruptCloseIterator (completion, iterated).
- Let completion be
- Set counter to counter + 1.
- Let value be ?
- Let result be
CreateIteratorFromClosure (closure,"Iterator Helper" ,%IteratorHelperPrototype% , « [[UnderlyingIterator]] »). - Set result.[[UnderlyingIterator]] to iterated.
- Return result.
27.1.4.5 Iterator.prototype.find ( predicate )
This method performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - Let iterated be the
Iterator Record { [[Iterator]]: O, [[NextMethod]]:undefined , [[Done]]:false }. - If
IsCallable (predicate) isfalse , then- Let error be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iterated, error).
- Let error be
- Set iterated to ?
GetIteratorDirect (O). - Let counter be 0.
- Repeat,
- Let value be ?
IteratorStepValue (iterated). - If value is
done , returnundefined . - Let result be
Completion (Call (predicate,undefined , « value,𝔽 (counter) »)). IfAbruptCloseIterator (result, iterated).- If
ToBoolean (result) istrue , return ?IteratorClose (iterated,NormalCompletion (value)). - Set counter to counter + 1.
- Let value be ?
27.1.4.6 Iterator.prototype.flatMap ( mapper )
This method performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - Let iterated be the
Iterator Record { [[Iterator]]: O, [[NextMethod]]:undefined , [[Done]]:false }. - If
IsCallable (mapper) isfalse , then- Let error be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iterated, error).
- Let error be
- Set iterated to ?
GetIteratorDirect (O). - Let closure be a new
Abstract Closure with no parameters that captures iterated and mapper and performs the following steps when called:- Let counter be 0.
- Repeat,
- Let value be ?
IteratorStepValue (iterated). - If value is
done , returnReturnCompletion (undefined ). - Let mapped be
Completion (Call (mapper,undefined , « value,𝔽 (counter) »)). IfAbruptCloseIterator (mapped, iterated).- Let innerIterator be
Completion (GetIteratorFlattenable (mapped,reject-primitives )). IfAbruptCloseIterator (innerIterator, iterated).- Let innerAlive be
true . - Repeat, while innerAlive is
true ,- Let innerValue be
Completion (IteratorStepValue (innerIterator)). IfAbruptCloseIterator (innerValue, iterated).- If innerValue is
done , then- Set innerAlive to
false .
- Set innerAlive to
- Else,
- Let completion be
Completion (Yield (innerValue)). - If completion is an
abrupt completion , then- Let backupCompletion be
Completion (IteratorClose (innerIterator, completion)). IfAbruptCloseIterator (backupCompletion, iterated).- Return ?
IteratorClose (iterated, completion).
- Let backupCompletion be
- Let completion be
- Let innerValue be
- Set counter to counter + 1.
- Let value be ?
- Let result be
CreateIteratorFromClosure (closure,"Iterator Helper" ,%IteratorHelperPrototype% , « [[UnderlyingIterator]] »). - Set result.[[UnderlyingIterator]] to iterated.
- Return result.
27.1.4.7 Iterator.prototype.forEach ( procedure )
This method performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - Let iterated be the
Iterator Record { [[Iterator]]: O, [[NextMethod]]:undefined , [[Done]]:false }. - If
IsCallable (procedure) isfalse , then- Let error be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iterated, error).
- Let error be
- Set iterated to ?
GetIteratorDirect (O). - Let counter be 0.
- Repeat,
- Let value be ?
IteratorStepValue (iterated). - If value is
done , returnundefined . - Let result be
Completion (Call (procedure,undefined , « value,𝔽 (counter) »)). IfAbruptCloseIterator (result, iterated).- Set counter to counter + 1.
- Let value be ?
27.1.4.8 Iterator.prototype.map ( mapper )
This method performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - Let iterated be the
Iterator Record { [[Iterator]]: O, [[NextMethod]]:undefined , [[Done]]:false }. - If
IsCallable (mapper) isfalse , then- Let error be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iterated, error).
- Let error be
- Set iterated to ?
GetIteratorDirect (O). - Let closure be a new
Abstract Closure with no parameters that captures iterated and mapper and performs the following steps when called:- Let counter be 0.
- Repeat,
- Let value be ?
IteratorStepValue (iterated). - If value is
done , returnReturnCompletion (undefined ). - Let mapped be
Completion (Call (mapper,undefined , « value,𝔽 (counter) »)). IfAbruptCloseIterator (mapped, iterated).- Let completion be
Completion (Yield (mapped)). IfAbruptCloseIterator (completion, iterated).- Set counter to counter + 1.
- Let value be ?
- Let result be
CreateIteratorFromClosure (closure,"Iterator Helper" ,%IteratorHelperPrototype% , « [[UnderlyingIterator]] »). - Set result.[[UnderlyingIterator]] to iterated.
- Return result.
27.1.4.9 Iterator.prototype.reduce ( reducer [ , initialValue ] )
This method performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - Let iterated be the
Iterator Record { [[Iterator]]: O, [[NextMethod]]:undefined , [[Done]]:false }. - If
IsCallable (reducer) isfalse , then- Let error be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iterated, error).
- Let error be
- Set iterated to ?
GetIteratorDirect (O). - If initialValue is not present, then
- Let accumulator be ?
IteratorStepValue (iterated). - If accumulator is
done , throw aTypeError exception. - Let counter be 1.
- Let accumulator be ?
- Else,
- Let accumulator be initialValue.
- Let counter be 0.
- Repeat,
- Let value be ?
IteratorStepValue (iterated). - If value is
done , return accumulator. - Let result be
Completion (Call (reducer,undefined , « accumulator, value,𝔽 (counter) »)). IfAbruptCloseIterator (result, iterated).- Set accumulator to result.
- Set counter to counter + 1.
- Let value be ?
27.1.4.10 Iterator.prototype.some ( predicate )
This method performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - Let iterated be the
Iterator Record { [[Iterator]]: O, [[NextMethod]]:undefined , [[Done]]:false }. - If
IsCallable (predicate) isfalse , then- Let error be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iterated, error).
- Let error be
- Set iterated to ?
GetIteratorDirect (O). - Let counter be 0.
- Repeat,
- Let value be ?
IteratorStepValue (iterated). - If value is
done , returnfalse . - Let result be
Completion (Call (predicate,undefined , « value,𝔽 (counter) »)). IfAbruptCloseIterator (result, iterated).- If
ToBoolean (result) istrue , return ?IteratorClose (iterated,NormalCompletion (true )). - Set counter to counter + 1.
- Let value be ?
27.1.4.11 Iterator.prototype.take ( limit )
This method performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - Let iterated be the
Iterator Record { [[Iterator]]: O, [[NextMethod]]:undefined , [[Done]]:false }. - Let numLimit be
Completion (ToNumber (limit)). IfAbruptCloseIterator (numLimit, iterated).- If numLimit is
NaN , then- Let error be
ThrowCompletion (a newly createdRangeError object). - Return ?
IteratorClose (iterated, error).
- Let error be
- Let integerLimit be !
ToIntegerOrInfinity (numLimit). - If integerLimit < 0, then
- Let error be
ThrowCompletion (a newly createdRangeError object). - Return ?
IteratorClose (iterated, error).
- Let error be
- Set iterated to ?
GetIteratorDirect (O). - Let closure be a new
Abstract Closure with no parameters that captures iterated and integerLimit and performs the following steps when called:- Let remaining be integerLimit.
- Repeat,
- If remaining = 0, then
- Return ?
IteratorClose (iterated,ReturnCompletion (undefined )).
- Return ?
- If remaining ≠ +∞, then
- Set remaining to remaining - 1.
- Let value be ?
IteratorStepValue (iterated). - If value is
done , returnReturnCompletion (undefined ). - Let completion be
Completion (Yield (value)). IfAbruptCloseIterator (completion, iterated).
- If remaining = 0, then
- Let result be
CreateIteratorFromClosure (closure,"Iterator Helper" ,%IteratorHelperPrototype% , « [[UnderlyingIterator]] »). - Set result.[[UnderlyingIterator]] to iterated.
- Return result.
27.1.4.12 Iterator.prototype.toArray ( )
This method performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - Let iterated be ?
GetIteratorDirect (O). - Let items be a new empty
List . - Repeat,
- Let value be ?
IteratorStepValue (iterated). - If value is
done , returnCreateArrayFromList (items). - Append value to items.
- Let value be ?
27.1.4.13 Iterator.prototype [ %Symbol.iterator% ] ( )
This function performs the following steps when called:
- Return the
this value.
The value of the
27.1.4.14 Iterator.prototype [ %Symbol.toStringTag% ]
Iterator.prototype[%Symbol.toStringTag%] is an
27.1.4.14.1 get Iterator.prototype [ %Symbol.toStringTag% ]
The value of the [[Get]] attribute is a built-in function that requires no arguments. It performs the following steps when called:
- Return
"Iterator" .
27.1.4.14.2 set Iterator.prototype [ %Symbol.toStringTag% ]
The value of the [[Set]] attribute is a built-in function that takes an argument v. It performs the following steps when called:
- Perform ?
SetterThatIgnoresPrototypeProperties (this value,%Iterator.prototype% ,%Symbol.toStringTag% , v). - Return
undefined .
Unlike the
27.1.5 The %AsyncIteratorPrototype% Object
The %AsyncIteratorPrototype% object:
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object .
All objects defined in this specification that implement the
27.1.5.1 %AsyncIteratorPrototype% [ %Symbol.asyncIterator% ] ( )
This function performs the following steps when called:
- Return the
this value.
The value of the
27.1.6 Async-from-Sync Iterator Objects
An Async-from-Sync Iterator
object is an
27.1.6.1 CreateAsyncFromSyncIterator ( syncIteratorRecord )
The abstract operation CreateAsyncFromSyncIterator takes argument
syncIteratorRecord (an
- Let asyncIterator be
OrdinaryObjectCreate (%AsyncFromSyncIteratorPrototype% , « [[SyncIteratorRecord]] »). - Set asyncIterator.[[SyncIteratorRecord]] to syncIteratorRecord.
- Let nextMethod be !
Get (asyncIterator,"next" ). - Let iteratorRecord be the
Iterator Record { [[Iterator]]: asyncIterator, [[NextMethod]]: nextMethod, [[Done]]:false }. - Return iteratorRecord.
27.1.6.2 The %AsyncFromSyncIteratorPrototype% Object
The %AsyncFromSyncIteratorPrototype% object:
- has properties that are inherited by all
Async-from-Sync Iterator objects . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%AsyncIteratorPrototype% . - is never directly accessible to ECMAScript code.
- has the following properties:
27.1.6.2.1 %AsyncFromSyncIteratorPrototype%.next ( [ value ] )
- Let O be the
this value. Assert : Ois an Object that has a [[SyncIteratorRecord]] internal slot.- Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let syncIteratorRecord be O.[[SyncIteratorRecord]].
- If value is present, then
- Let result be
Completion (IteratorNext (syncIteratorRecord, value)).
- Let result be
- Else,
- Let result be
Completion (IteratorNext (syncIteratorRecord)).
- Let result be
IfAbruptRejectPromise (result, promiseCapability).- Return
AsyncFromSyncIteratorContinuation (result, promiseCapability, syncIteratorRecord,true ).
27.1.6.2.2 %AsyncFromSyncIteratorPrototype%.return ( [ value ] )
- Let O be the
this value. Assert : Ois an Object that has a [[SyncIteratorRecord]] internal slot.- Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let syncIteratorRecord be O.[[SyncIteratorRecord]].
- Let syncIterator be syncIteratorRecord.[[Iterator]].
- Let return be
Completion (GetMethod (syncIterator,"return" )). IfAbruptRejectPromise (return, promiseCapability).- If return is
undefined , then- Let iteratorResult be
CreateIteratorResultObject (value,true ). - Perform ! Call(promiseCapability.[[Resolve]],
undefined , « iteratorResult »). - Return promiseCapability.[[Promise]].
- Let iteratorResult be
- If value is present, then
- Let result be
Completion (Call (return, syncIterator, « value »)).
- Let result be
- Else,
- Let result be
Completion (Call (return, syncIterator)).
- Let result be
IfAbruptRejectPromise (result, promiseCapability).- If result
is not an Object , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « a newly createdTypeError object »). - Return promiseCapability.[[Promise]].
- Perform !
- Return
AsyncFromSyncIteratorContinuation (result, promiseCapability, syncIteratorRecord,false ).
27.1.6.2.3 %AsyncFromSyncIteratorPrototype%.throw ( [ value ] )
- Let O be the
this value. Assert : Ois an Object that has a [[SyncIteratorRecord]] internal slot.- Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let syncIteratorRecord be O.[[SyncIteratorRecord]].
- Let syncIterator be syncIteratorRecord.[[Iterator]].
- Let throw be
Completion (GetMethod (syncIterator,"throw" )). IfAbruptRejectPromise (throw, promiseCapability).- If throw is
undefined , then- NOTE: If syncIterator does not have a
throwmethod, close it to give it a chance to clean up before we reject the capability. - Let closeCompletion be
NormalCompletion (empty ). - Let result be
Completion (IteratorClose (syncIteratorRecord, closeCompletion)). IfAbruptRejectPromise (result, promiseCapability).- NOTE: The next step throws a
TypeError to indicate that there was a protocol violation: syncIterator does not have athrowmethod. - NOTE: If closing syncIterator does not throw then the result of that operation is ignored, even if it yields a rejected promise.
- Perform !
Call (promiseCapability.[[Reject]],undefined , « a newly createdTypeError object »). - Return promiseCapability.[[Promise]].
- NOTE: If syncIterator does not have a
- If value is present, then
- Let result be
Completion (Call (throw, syncIterator, « value »)).
- Let result be
- Else,
- Let result be
Completion (Call (throw, syncIterator)).
- Let result be
IfAbruptRejectPromise (result, promiseCapability).- If result
is not an Object , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « a newly createdTypeError object »). - Return promiseCapability.[[Promise]].
- Perform !
- Return
AsyncFromSyncIteratorContinuation (result, promiseCapability, syncIteratorRecord,true ).
27.1.6.3 Properties of Async-from-Sync Iterator Instances
Async-from-Sync
| Internal Slot | Type | Description |
|---|---|---|
| [[SyncIteratorRecord]] |
an |
Represents the original synchronous |
27.1.6.4 AsyncFromSyncIteratorContinuation ( result, promiseCapability, syncIteratorRecord, closeOnRejection )
The abstract operation AsyncFromSyncIteratorContinuation takes arguments result
(an Object), promiseCapability (a
- NOTE: Because promiseCapability is derived from the intrinsic
%Promise% , the calls to promiseCapability.[[Reject]] entailed by the useIfAbruptRejectPromise below are guaranteed not to throw. - Let done be
Completion (IteratorComplete (result)). IfAbruptRejectPromise (done, promiseCapability).- Let value be
Completion (IteratorValue (result)). IfAbruptRejectPromise (value, promiseCapability).- Let valueWrapper be
Completion (PromiseResolve (%Promise% , value)). - If valueWrapper is an
abrupt completion , done isfalse , and closeOnRejection istrue , then- Set valueWrapper to
Completion (IteratorClose (syncIteratorRecord, valueWrapper)).
- Set valueWrapper to
IfAbruptRejectPromise (valueWrapper, promiseCapability).- Let unwrap be a new
Abstract Closure with parameters (v) that captures done and performs the following steps when called:- Return
CreateIteratorResultObject (v, done).
- Return
- Let onFulfilled be
CreateBuiltinFunction (unwrap, 1,"" , « »). - NOTE: onFulfilled is used when processing the
"value" property of anIteratorResult object in order to wait for its value if it is a promise and re-package the result in a new "unwrapped"IteratorResult object . - If done is
true , or if closeOnRejection isfalse , then- Let onRejected be
undefined .
- Let onRejected be
- Else,
- Let closeIterator be a new
Abstract Closure with parameters (error) that captures syncIteratorRecord and performs the following steps when called:- Return ?
IteratorClose (syncIteratorRecord,ThrowCompletion (error)).
- Return ?
- Let onRejected be
CreateBuiltinFunction (closeIterator, 1,"" , « »). - NOTE: onRejected is used to close the
Iterator when the"value" property of anIteratorResult object it yields is a rejected promise.
- Let closeIterator be a new
- Perform
PerformPromiseThen (valueWrapper, onFulfilled, onRejected, promiseCapability). - Return promiseCapability.[[Promise]].
27.2 Promise Objects
A Promise is an object that is used as a placeholder for the eventual results of a deferred (and possibly asynchronous) computation.
Any Promise is in one of three mutually exclusive states: fulfilled, rejected, and pending:
-
A promise
pis fulfilled ifp.then(f, r)will immediately enqueue aJob to call the functionf. -
A promise
pis rejected ifp.then(f, r)will immediately enqueue aJob to call the functionr. - A promise is pending if it is neither fulfilled nor rejected.
A promise is said to be settled if it is not pending, i.e. if it is either fulfilled or rejected.
A promise is resolved if it is settled or if it has been “locked in” to match the state of another promise. Attempting to resolve or reject a resolved promise has no effect. A promise is unresolved if it is not resolved. An unresolved promise is always in the pending state. A resolved promise may be pending, fulfilled or rejected.
27.2.1 Promise Abstract Operations
27.2.1.1 PromiseCapability Records
A PromiseCapability Record is a
PromiseCapability Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Promise]] | an Object | An object that is usable as a promise. |
| [[Resolve]] |
a |
The function that is used to resolve the given promise. |
| [[Reject]] |
a |
The function that is used to reject the given promise. |
27.2.1.1.1 IfAbruptRejectPromise ( value, capability )
IfAbruptRejectPromise is a shorthand for a sequence of algorithm steps that use a
IfAbruptRejectPromise (value, capability).
means the same thing as:
Assert : value is aCompletion Record .- If value is an
abrupt completion , then- Perform ?
Call (capability.[[Reject]],undefined , « value.[[Value]] »). - Return capability.[[Promise]].
- Perform ?
- Else,
- Set value to ! value.
27.2.1.2 PromiseReaction Records
A PromiseReaction Record is a
PromiseReaction Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Capability]] |
a |
The capabilities of the promise for which this record provides a reaction handler. |
| [[Type]] |
|
The [[Type]] is used when [[Handler]] is |
| [[Handler]] |
a |
The function that should be applied to the incoming value, and whose
return value will govern what happens to the derived promise. If [[Handler]] is |
27.2.1.3 CreateResolvingFunctions ( promise )
The abstract operation CreateResolvingFunctions takes argument promise (a Promise)
and returns a
- Let alreadyResolved be the
Record { [[Value]]:false }. - Let stepsResolve be the algorithm steps defined in
Promise Resolve Functions . - Let lengthResolve be the number of non-optional parameters of the
function definition in
Promise Resolve Functions . - Let resolve be
CreateBuiltinFunction (stepsResolve, lengthResolve,"" , « [[Promise]], [[AlreadyResolved]] »). - Set resolve.[[Promise]] to promise.
- Set resolve.[[AlreadyResolved]] to alreadyResolved.
- Let stepsReject be the algorithm steps defined in
Promise Reject Functions . - Let lengthReject be the number of non-optional parameters of the function
definition in
Promise Reject Functions . - Let reject be
CreateBuiltinFunction (stepsReject, lengthReject,"" , « [[Promise]], [[AlreadyResolved]] »). - Set reject.[[Promise]] to promise.
- Set reject.[[AlreadyResolved]] to alreadyResolved.
- Return the
Record { [[Resolve]]: resolve, [[Reject]]: reject }.
27.2.1.3.1 Promise Reject Functions
A promise reject function is an anonymous built-in function that has [[Promise]] and [[AlreadyResolved]] internal slots.
When a promise reject function is called with argument reason, the following steps are taken:
- Let F be the
active function object . Assert : F has a [[Promise]] internal slot whose valueis an Object .- Let promise be F.[[Promise]].
- Let alreadyResolved be F.[[AlreadyResolved]].
- If alreadyResolved.[[Value]] is
true , returnundefined . - Set alreadyResolved.[[Value]] to
true . - Perform
RejectPromise (promise, reason). - Return
undefined .
The
27.2.1.3.2 Promise Resolve Functions
A promise resolve function is an anonymous built-in function that has [[Promise]] and [[AlreadyResolved]] internal slots.
When a promise resolve function is called with argument resolution, the following steps are taken:
- Let F be the
active function object . Assert : F has a [[Promise]] internal slot whose valueis an Object .- Let promise be F.[[Promise]].
- Let alreadyResolved be F.[[AlreadyResolved]].
- If alreadyResolved.[[Value]] is
true , returnundefined . - Set alreadyResolved.[[Value]] to
true . - If
SameValue (resolution, promise) istrue , then- Let selfResolutionError be a newly created
TypeError object. - Perform
RejectPromise (promise, selfResolutionError). - Return
undefined .
- Let selfResolutionError be a newly created
- If resolution
is not an Object , then- Perform
FulfillPromise (promise, resolution). - Return
undefined .
- Perform
- Let then be
Completion (Get (resolution,"then" )). - If then is an
abrupt completion , then- Perform
RejectPromise (promise, then.[[Value]]). - Return
undefined .
- Perform
- Let thenAction be then.[[Value]].
- If
IsCallable (thenAction) isfalse , then- Perform
FulfillPromise (promise, resolution). - Return
undefined .
- Perform
- Let thenJobCallback be
HostMakeJobCallback (thenAction). - Let job be
NewPromiseResolveThenableJob (promise, resolution, thenJobCallback). - Perform
HostEnqueuePromiseJob (job.[[Job]], job.[[Realm]]). - Return
undefined .
The
27.2.1.4 FulfillPromise ( promise, value )
The abstract operation FulfillPromise takes arguments promise (a Promise) and
value (an
Assert : promise.[[PromiseState]] ispending .- Let reactions be promise.[[PromiseFulfillReactions]].
- Set promise.[[PromiseResult]] to value.
- Set promise.[[PromiseFulfillReactions]] to
undefined . - Set promise.[[PromiseRejectReactions]] to
undefined . - Set promise.[[PromiseState]] to
fulfilled . - Perform
TriggerPromiseReactions (reactions, value). - Return
unused .
27.2.1.5 NewPromiseCapability ( C )
The abstract operation NewPromiseCapability takes argument C (an resolve and reject functions. The promise plus the
resolve and reject functions are used to initialize a new
- If
IsConstructor (C) isfalse , throw aTypeError exception. - NOTE: C is assumed to be a
constructor function that supports the parameter conventions of the Promiseconstructor (see27.2.3.1 ). - Let resolvingFunctions be the
Record { [[Resolve]]:undefined , [[Reject]]:undefined }. - Let executorClosure be a new
Abstract Closure with parameters (resolve, reject) that captures resolvingFunctions and performs the following steps when called:- If resolvingFunctions.[[Resolve]] is not
undefined , throw aTypeError exception. - If resolvingFunctions.[[Reject]] is not
undefined , throw aTypeError exception. - Set resolvingFunctions.[[Resolve]] to resolve.
- Set resolvingFunctions.[[Reject]] to reject.
- Return
NormalCompletion (undefined ).
- If resolvingFunctions.[[Resolve]] is not
- Let executor be
CreateBuiltinFunction (executorClosure, 2,"" , « »). - Let promise be ?
Construct (C, « executor »). - If
IsCallable (resolvingFunctions.[[Resolve]]) isfalse , throw aTypeError exception. - If
IsCallable (resolvingFunctions.[[Reject]]) isfalse , throw aTypeError exception. - Return the
PromiseCapability Record { [[Promise]]: promise, [[Resolve]]: resolvingFunctions.[[Resolve]], [[Reject]]: resolvingFunctions.[[Reject]] }.
This abstract operation supports Promise subclassing, as it is generic on any
27.2.1.6 IsPromise ( x )
The abstract operation IsPromise takes argument x (an
- If x
is not an Object , returnfalse . - If x does not have a [[PromiseState]] internal
slot, return
false . - Return
true .
27.2.1.7 RejectPromise ( promise, reason )
The abstract operation RejectPromise takes arguments promise (a Promise) and
reason (an
Assert : promise.[[PromiseState]] ispending .- Let reactions be promise.[[PromiseRejectReactions]].
- Set promise.[[PromiseResult]] to reason.
- Set promise.[[PromiseFulfillReactions]] to
undefined . - Set promise.[[PromiseRejectReactions]] to
undefined . - Set promise.[[PromiseState]] to
rejected . - If promise.[[PromiseIsHandled]] is
false , performHostPromiseRejectionTracker (promise,"reject" ). - Perform
TriggerPromiseReactions (reactions, reason). - Return
unused .
27.2.1.8 TriggerPromiseReactions ( reactions, argument )
The abstract operation TriggerPromiseReactions takes arguments reactions (a
- For each element reaction of reactions, do
- Let job be
NewPromiseReactionJob (reaction, argument). - Perform
HostEnqueuePromiseJob (job.[[Job]], job.[[Realm]]).
- Let job be
- Return
unused .
27.2.1.9 HostPromiseRejectionTracker ( promise, operation )
The
The default implementation of HostPromiseRejectionTracker is to return
HostPromiseRejectionTracker is called in two scenarios:
- When a promise is rejected without any handlers, it is called with its
operation argument set to
"reject" . - When a handler is added to a rejected promise for the first time, it is called
with its operation argument set to
"handle" .
A typical implementation of HostPromiseRejectionTracker might try to notify developers of unhandled rejections, while also being careful to notify them if such previous notifications are later invalidated by new handlers being attached.
If operation is
27.2.2 Promise Jobs
27.2.2.1 NewPromiseReactionJob ( reaction, argument )
The abstract operation NewPromiseReactionJob takes arguments reaction (a
- Let job be a new
Job Abstract Closure with no parameters that captures reaction and argument and performs the following steps when called:- Let promiseCapability be reaction.[[Capability]].
- Let type be reaction.[[Type]].
- Let handler be reaction.[[Handler]].
- If handler is
empty , then- If type is
fulfill , then- Let handlerResult be
NormalCompletion (argument).
- Let handlerResult be
- Else,
Assert : type isreject .- Let handlerResult be
ThrowCompletion (argument).
- If type is
- Else,
- Let handlerResult be
Completion (HostCallJobCallback (handler,undefined , « argument »)).
- Let handlerResult be
- If promiseCapability is
undefined , thenAssert : handlerResult is not anabrupt completion .- Return
empty .
Assert : promiseCapability is aPromiseCapability Record .- If handlerResult is an
abrupt completion , then- Return ?
Call (promiseCapability.[[Reject]],undefined , « handlerResult.[[Value]] »).
- Return ?
- Else,
- Return ?
Call (promiseCapability.[[Resolve]],undefined , « handlerResult.[[Value]] »).
- Return ?
- Let handlerRealm be
null . - If reaction.[[Handler]] is not
empty , then- Let getHandlerRealmResult be
Completion (GetFunctionRealm (reaction.[[Handler]].[[Callback]])). - If getHandlerRealmResult is a
normal completion , set handlerRealm to getHandlerRealmResult.[[Value]]. - Else, set handlerRealm to
the current Realm Record . - NOTE: handlerRealm is never
null unless the handler isundefined . When the handler is a revoked Proxy and no ECMAScript code runs, handlerRealm is used to create error objects.
- Let getHandlerRealmResult be
- Return the
Record { [[Job]]: job, [[Realm]]: handlerRealm }.
27.2.2.2 NewPromiseResolveThenableJob ( promiseToResolve, thenable, then )
The abstract operation NewPromiseResolveThenableJob takes arguments
promiseToResolve (a Promise), thenable (an Object), and
then (a
- Let job be a new
Job Abstract Closure with no parameters that captures promiseToResolve, thenable, and then and performs the following steps when called:- Let resolvingFunctions be
CreateResolvingFunctions (promiseToResolve). - Let thenCallResult be
Completion (HostCallJobCallback (then, thenable, « resolvingFunctions.[[Resolve]], resolvingFunctions.[[Reject]] »)). - If thenCallResult is an
abrupt completion , then- Return ?
Call (resolvingFunctions.[[Reject]],undefined , « thenCallResult.[[Value]] »).
- Return ?
- Return ! thenCallResult.
- Let resolvingFunctions be
- Let getThenRealmResult be
Completion (GetFunctionRealm (then.[[Callback]])). - If getThenRealmResult is a
normal completion , let thenRealm be getThenRealmResult.[[Value]]. - Else, let thenRealm be
the current Realm Record . - NOTE: thenRealm is never
null . When then.[[Callback]] is a revoked Proxy and no code runs, thenRealm is used to create error objects. - Return the
Record { [[Job]]: job, [[Realm]]: thenRealm }.
27.2.3 The Promise Constructor
The Promise
- is %Promise%.
- is the initial value of the
"Promise" property of theglobal object . - creates and initializes a new Promise when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Promise behaviour must include asupercall to the Promiseconstructor to create and initialize the subclass instance with the internal state necessary to support thePromiseandPromise.prototypebuilt-in methods.
27.2.3.1 Promise ( executor )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - If
IsCallable (executor) isfalse , throw aTypeError exception. - Let promise be ?
OrdinaryCreateFromConstructor (NewTarget,"%Promise.prototype%" , « [[PromiseState]], [[PromiseResult]], [[PromiseFulfillReactions]], [[PromiseRejectReactions]], [[PromiseIsHandled]] »). - Set promise.[[PromiseState]] to
pending . - Set promise.[[PromiseResult]] to
empty . - Set promise.[[PromiseFulfillReactions]] to a new
empty
List . - Set promise.[[PromiseRejectReactions]] to a new
empty
List . - Set promise.[[PromiseIsHandled]] to
false . - Let resolvingFunctions be
CreateResolvingFunctions (promise). - Let completion be
Completion (Call (executor,undefined , « resolvingFunctions.[[Resolve]], resolvingFunctions.[[Reject]] »)). - If completion is an
abrupt completion , then- Perform ?
Call (resolvingFunctions.[[Reject]],undefined , « completion.[[Value]] »).
- Perform ?
- Return promise.
The executor argument must be a
The resolve function that is passed to an executor function accepts a single argument. The executor code may eventually call the resolve function to indicate that it wishes to resolve the associated Promise. The argument passed to the resolve function represents the eventual value of the deferred action and can be either the actual fulfillment value or another promise which will provide the value if it is fulfilled.
The reject function that is passed to an executor function accepts a single argument. The executor code may eventually call the reject function to indicate that the associated Promise is rejected and will never be fulfilled. The argument passed to the reject function is used as the rejection value of the promise. Typically it will be an Error object.
The resolve and reject functions passed to an executor function by the
Promise
27.2.4 Properties of the Promise Constructor
The Promise
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
27.2.4.1 Promise.all ( iterable )
This function returns a new promise which is fulfilled with an array of fulfillment values
for the passed promises, or rejects with the reason of the first passed promise that
rejects. It resolves all elements of the passed
- Let C be the
this value. - Let promiseCapability be ?
NewPromiseCapability (C). - Let promiseResolve be
Completion (GetPromiseResolve (C)). IfAbruptRejectPromise (promiseResolve, promiseCapability).- Let iteratorRecord be
Completion (GetIterator (iterable,sync )). IfAbruptRejectPromise (iteratorRecord, promiseCapability).- Let result be
Completion (PerformPromiseAll (iteratorRecord, C, promiseCapability, promiseResolve)). - If result is an
abrupt completion , then- If iteratorRecord.[[Done]] is
false , set result toCompletion (IteratorClose (iteratorRecord, result)). IfAbruptRejectPromise (result, promiseCapability).
- If iteratorRecord.[[Done]] is
- Return ! result.
This function requires its
27.2.4.1.1 GetPromiseResolve ( promiseConstructor )
The abstract operation GetPromiseResolve takes argument promiseConstructor (a
- Let promiseResolve be ?
Get (promiseConstructor,"resolve" ). - If
IsCallable (promiseResolve) isfalse , throw aTypeError exception. - Return promiseResolve.
27.2.4.1.2 PerformPromiseAll ( iteratorRecord, constructor, resultCapability, promiseResolve )
The abstract operation PerformPromiseAll takes arguments iteratorRecord (an
- Let values be a new empty
List . - Let remainingElementsCount be the
Record { [[Value]]: 1 }. - Let index be 0.
- Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , then- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] - 1.
- If remainingElementsCount.[[Value]] = 0, then
- Let valuesArray be
CreateArrayFromList (values). - Perform ?
Call (resultCapability.[[Resolve]],undefined , « valuesArray »).
- Let valuesArray be
- Return resultCapability.[[Promise]].
- Append
undefined to values. - Let nextPromise be ?
Call (promiseResolve, constructor, « next »). - Let steps be the algorithm steps defined in
Promise.allResolve Element Functions - Let length be the number of non-optional parameters of the
function definition in
Promise.allResolve Element Functions - Let onFulfilled be
CreateBuiltinFunction (steps, length,"" , « [[AlreadyCalled]], [[Index]], [[Values]], [[Capability]], [[RemainingElements]] »). - Set onFulfilled.[[AlreadyCalled]] to
false . - Set onFulfilled.[[Index]] to index.
- Set onFulfilled.[[Values]] to values.
- Set onFulfilled.[[Capability]] to resultCapability.
- Set onFulfilled.[[RemainingElements]] to remainingElementsCount.
- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] + 1.
- Perform ?
Invoke (nextPromise,"then" , « onFulfilled, resultCapability.[[Reject]] »). - Set index to index + 1.
- Let next be ?
27.2.4.1.3 Promise.all Resolve Element
Functions
A Promise.all resolve element function is an anonymous built-in function
that is used to resolve a specific Promise.all element. Each
Promise.all resolve element function has [[Index]], [[Values]], [[Capability]], [[RemainingElements]],
and [[AlreadyCalled]] internal slots.
When a Promise.all resolve element function is called with argument
x, the following steps are taken:
- Let F be the
active function object . - If F.[[AlreadyCalled]] is
true , returnundefined . - Set F.[[AlreadyCalled]] to
true . - Let index be F.[[Index]].
- Let values be F.[[Values]].
- Let promiseCapability be F.[[Capability]].
- Let remainingElementsCount be F.[[RemainingElements]].
- Set values[index] to x.
- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] - 1.
- If remainingElementsCount.[[Value]] = 0,
then
- Let valuesArray be
CreateArrayFromList (values). - Return ?
Call (promiseCapability.[[Resolve]],undefined , « valuesArray »).
- Let valuesArray be
- Return
undefined .
The Promise.all resolve element
function is
27.2.4.2 Promise.allSettled ( iterable )
This function returns a promise that is fulfilled with an array of promise state snapshots,
but only after all the original promises have settled, i.e. become either fulfilled or
rejected. It resolves all elements of the passed
- Let C be the
this value. - Let promiseCapability be ?
NewPromiseCapability (C). - Let promiseResolve be
Completion (GetPromiseResolve (C)). IfAbruptRejectPromise (promiseResolve, promiseCapability).- Let iteratorRecord be
Completion (GetIterator (iterable,sync )). IfAbruptRejectPromise (iteratorRecord, promiseCapability).- Let result be
Completion (PerformPromiseAllSettled (iteratorRecord, C, promiseCapability, promiseResolve)). - If result is an
abrupt completion , then- If iteratorRecord.[[Done]] is
false , set result toCompletion (IteratorClose (iteratorRecord, result)). IfAbruptRejectPromise (result, promiseCapability).
- If iteratorRecord.[[Done]] is
- Return ! result.
This function requires its
27.2.4.2.1 PerformPromiseAllSettled ( iteratorRecord, constructor, resultCapability, promiseResolve )
The abstract operation PerformPromiseAllSettled takes arguments iteratorRecord
(an
- Let values be a new empty
List . - Let remainingElementsCount be the
Record { [[Value]]: 1 }. - Let index be 0.
- Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , then- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] - 1.
- If remainingElementsCount.[[Value]] = 0, then
- Let valuesArray be
CreateArrayFromList (values). - Perform ?
Call (resultCapability.[[Resolve]],undefined , « valuesArray »).
- Let valuesArray be
- Return resultCapability.[[Promise]].
- Append
undefined to values. - Let nextPromise be ?
Call (promiseResolve, constructor, « next »). - Let stepsFulfilled be the algorithm steps defined in
Promise.allSettledResolve Element Functions - Let lengthFulfilled be the number of non-optional parameters
of the function definition in
Promise.allSettledResolve Element Functions - Let onFulfilled be
CreateBuiltinFunction (stepsFulfilled, lengthFulfilled,"" , « [[AlreadyCalled]], [[Index]], [[Values]], [[Capability]], [[RemainingElements]] »). - Let alreadyCalled be the
Record { [[Value]]:false }. - Set onFulfilled.[[AlreadyCalled]] to alreadyCalled.
- Set onFulfilled.[[Index]] to index.
- Set onFulfilled.[[Values]] to values.
- Set onFulfilled.[[Capability]] to resultCapability.
- Set onFulfilled.[[RemainingElements]] to remainingElementsCount.
- Let stepsRejected be the algorithm steps defined in
Promise.allSettledReject Element Functions - Let lengthRejected be the number of non-optional parameters
of the function definition in
Promise.allSettledReject Element Functions - Let onRejected be
CreateBuiltinFunction (stepsRejected, lengthRejected,"" , « [[AlreadyCalled]], [[Index]], [[Values]], [[Capability]], [[RemainingElements]] »). - Set onRejected.[[AlreadyCalled]] to alreadyCalled.
- Set onRejected.[[Index]] to index.
- Set onRejected.[[Values]] to values.
- Set onRejected.[[Capability]] to resultCapability.
- Set onRejected.[[RemainingElements]] to remainingElementsCount.
- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] + 1.
- Perform ?
Invoke (nextPromise,"then" , « onFulfilled, onRejected »). - Set index to index + 1.
- Let next be ?
27.2.4.2.2 Promise.allSettled Resolve Element
Functions
A Promise.allSettled resolve element function is an anonymous built-in
function that is used to resolve a specific Promise.allSettled element.
Each Promise.allSettled resolve element function has [[Index]], [[Values]], [[Capability]], [[RemainingElements]],
and [[AlreadyCalled]] internal slots.
When a Promise.allSettled resolve element function is called with argument
x, the following steps are taken:
- Let F be the
active function object . - Let alreadyCalled be F.[[AlreadyCalled]].
- If alreadyCalled.[[Value]] is
true , returnundefined . - Set alreadyCalled.[[Value]] to
true . - Let index be F.[[Index]].
- Let values be F.[[Values]].
- Let promiseCapability be F.[[Capability]].
- Let remainingElementsCount be F.[[RemainingElements]].
- Let obj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (obj,"status" ,"fulfilled" ). - Perform !
CreateDataPropertyOrThrow (obj,"value" , x). - Set values[index] to obj.
- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] - 1.
- If remainingElementsCount.[[Value]] = 0,
then
- Let valuesArray be
CreateArrayFromList (values). - Return ?
Call (promiseCapability.[[Resolve]],undefined , « valuesArray »).
- Let valuesArray be
- Return
undefined .
The Promise.allSettled resolve
element function is
27.2.4.2.3 Promise.allSettled Reject Element
Functions
A Promise.allSettled reject element function is an anonymous built-in
function that is used to reject a specific Promise.allSettled element. Each
Promise.allSettled reject element function has [[Index]], [[Values]], [[Capability]], [[RemainingElements]],
and [[AlreadyCalled]] internal slots.
When a Promise.allSettled reject element function is called with argument
x, the following steps are taken:
- Let F be the
active function object . - Let alreadyCalled be F.[[AlreadyCalled]].
- If alreadyCalled.[[Value]] is
true , returnundefined . - Set alreadyCalled.[[Value]] to
true . - Let index be F.[[Index]].
- Let values be F.[[Values]].
- Let promiseCapability be F.[[Capability]].
- Let remainingElementsCount be F.[[RemainingElements]].
- Let obj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (obj,"status" ,"rejected" ). - Perform !
CreateDataPropertyOrThrow (obj,"reason" , x). - Set values[index] to obj.
- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] - 1.
- If remainingElementsCount.[[Value]] = 0,
then
- Let valuesArray be
CreateArrayFromList (values). - Return ?
Call (promiseCapability.[[Resolve]],undefined , « valuesArray »).
- Let valuesArray be
- Return
undefined .
The Promise.allSettled reject
element function is
27.2.4.3 Promise.any ( iterable )
This function returns a promise that is fulfilled by the first given promise to be fulfilled,
or rejected with an AggregateError holding the rejection reasons if all of the
given promises are rejected. It resolves all elements of the passed
- Let C be the
this value. - Let promiseCapability be ?
NewPromiseCapability (C). - Let promiseResolve be
Completion (GetPromiseResolve (C)). IfAbruptRejectPromise (promiseResolve, promiseCapability).- Let iteratorRecord be
Completion (GetIterator (iterable,sync )). IfAbruptRejectPromise (iteratorRecord, promiseCapability).- Let result be
Completion (PerformPromiseAny (iteratorRecord, C, promiseCapability, promiseResolve)). - If result is an
abrupt completion , then- If iteratorRecord.[[Done]] is
false , set result toCompletion (IteratorClose (iteratorRecord, result)). IfAbruptRejectPromise (result, promiseCapability).
- If iteratorRecord.[[Done]] is
- Return ! result.
This function requires its Promise
27.2.4.3.1 PerformPromiseAny ( iteratorRecord, constructor, resultCapability, promiseResolve )
The abstract operation PerformPromiseAny takes arguments iteratorRecord (an
- Let errors be a new empty
List . - Let remainingElementsCount be the
Record { [[Value]]: 1 }. - Let index be 0.
- Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , then- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] - 1.
- If remainingElementsCount.[[Value]] = 0, then
- Let error be a newly created
AggregateError object. - Perform !
DefinePropertyOrThrow (error,"errors" , PropertyDescriptor { [[Configurable]]:true , [[Enumerable]]:false , [[Writable]]:true , [[Value]]:CreateArrayFromList (errors) }). - Return
ThrowCompletion (error).
- Let error be a newly created
- Return resultCapability.[[Promise]].
- Append
undefined to errors. - Let nextPromise be ?
Call (promiseResolve, constructor, « next »). - Let stepsRejected be the algorithm steps defined in
Promise.anyReject Element Functions - Let lengthRejected be the number of non-optional parameters
of the function definition in
Promise.anyReject Element Functions - Let onRejected be
CreateBuiltinFunction (stepsRejected, lengthRejected,"" , « [[AlreadyCalled]], [[Index]], [[Errors]], [[Capability]], [[RemainingElements]] »). - Set onRejected.[[AlreadyCalled]] to
false . - Set onRejected.[[Index]] to index.
- Set onRejected.[[Errors]] to errors.
- Set onRejected.[[Capability]] to resultCapability.
- Set onRejected.[[RemainingElements]] to remainingElementsCount.
- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] + 1.
- Perform ?
Invoke (nextPromise,"then" , « resultCapability.[[Resolve]], onRejected »). - Set index to index + 1.
- Let next be ?
27.2.4.3.2 Promise.any Reject Element Functions
A Promise.any reject element function is an anonymous built-in function that
is used to reject a specific Promise.any element. Each
Promise.any reject element function has [[Index]],
[[Errors]], [[Capability]], [[RemainingElements]], and [[AlreadyCalled]] internal slots.
When a Promise.any reject element function is called with argument
x, the following steps are taken:
- Let F be the
active function object . - If F.[[AlreadyCalled]] is
true , returnundefined . - Set F.[[AlreadyCalled]] to
true . - Let index be F.[[Index]].
- Let errors be F.[[Errors]].
- Let promiseCapability be F.[[Capability]].
- Let remainingElementsCount be F.[[RemainingElements]].
- Set errors[index] to x.
- Set remainingElementsCount.[[Value]] to remainingElementsCount.[[Value]] - 1.
- If remainingElementsCount.[[Value]] = 0,
then
- Let error be a newly created
AggregateError object. - Perform !
DefinePropertyOrThrow (error,"errors" , PropertyDescriptor { [[Configurable]]:true , [[Enumerable]]:false , [[Writable]]:true , [[Value]]:CreateArrayFromList (errors) }). - Return ?
Call (promiseCapability.[[Reject]],undefined , « error »).
- Let error be a newly created
- Return
undefined .
The Promise.any reject element
function is
27.2.4.4 Promise.prototype
The initial value of Promise.prototype is the
This property has the attributes { [[Writable]]:
27.2.4.5 Promise.race ( iterable )
This function returns a new promise which is settled in the same way as the first passed promise to settle. It resolves all elements of the passed iterable to promises as it runs this algorithm.
- Let C be the
this value. - Let promiseCapability be ?
NewPromiseCapability (C). - Let promiseResolve be
Completion (GetPromiseResolve (C)). IfAbruptRejectPromise (promiseResolve, promiseCapability).- Let iteratorRecord be
Completion (GetIterator (iterable,sync )). IfAbruptRejectPromise (iteratorRecord, promiseCapability).- Let result be
Completion (PerformPromiseRace (iteratorRecord, C, promiseCapability, promiseResolve)). - If result is an
abrupt completion , then- If iteratorRecord.[[Done]] is
false , set result toCompletion (IteratorClose (iteratorRecord, result)). IfAbruptRejectPromise (result, promiseCapability).
- If iteratorRecord.[[Done]] is
- Return ! result.
If the iterable argument yields no values or if none of the promises yielded by iterable ever settle, then the pending promise returned by this method will never be settled.
This function expects its resolve
method.
27.2.4.5.1 PerformPromiseRace ( iteratorRecord, constructor, resultCapability, promiseResolve )
The abstract operation PerformPromiseRace takes arguments iteratorRecord (an
- Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , then- Return resultCapability.[[Promise]].
- Let nextPromise be ?
Call (promiseResolve, constructor, « next »). - Perform ?
Invoke (nextPromise,"then" , « resultCapability.[[Resolve]], resultCapability.[[Reject]] »).
- Let next be ?
27.2.4.6 Promise.reject ( r )
This function returns a new promise rejected with the passed argument.
- Let C be the
this value. - Let promiseCapability be ?
NewPromiseCapability (C). - Perform ?
Call (promiseCapability.[[Reject]],undefined , « r »). - Return promiseCapability.[[Promise]].
This function expects its
27.2.4.7 Promise.resolve ( x )
This function returns either a new promise resolved with the passed argument, or the argument
itself if the argument is a promise produced by this
- Let C be the
this value. - If C
is not an Object , throw aTypeError exception. - Return ?
PromiseResolve (C, x).
This function expects its
27.2.4.7.1 PromiseResolve ( C, x )
The abstract operation PromiseResolve takes arguments C (an Object) and
x (an
- If
IsPromise (x) istrue , then - Let promiseCapability be ?
NewPromiseCapability (C). - Perform ?
Call (promiseCapability.[[Resolve]],undefined , « x »). - Return promiseCapability.[[Promise]].
27.2.4.8 Promise.try ( callback, ...args )
This function performs the following steps when called:
- Let C be the
this value. - If C
is not an Object , throw aTypeError exception. - Let promiseCapability be ?
NewPromiseCapability (C). - Let status be
Completion (Call (callback,undefined , args)). - If status is an
abrupt completion , then- Perform ?
Call (promiseCapability.[[Reject]],undefined , « status.[[Value]] »).
- Perform ?
- Else,
- Perform ?
Call (promiseCapability.[[Resolve]],undefined , « status.[[Value]] »).
- Perform ?
- Return promiseCapability.[[Promise]].
This function expects its
27.2.4.9 Promise.withResolvers ( )
This function returns an object with three properties: a new promise together with the
resolve and reject functions associated with it.
- Let C be the
this value. - Let promiseCapability be ?
NewPromiseCapability (C). - Let obj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (obj,"promise" , promiseCapability.[[Promise]]). - Perform !
CreateDataPropertyOrThrow (obj,"resolve" , promiseCapability.[[Resolve]]). - Perform !
CreateDataPropertyOrThrow (obj,"reject" , promiseCapability.[[Reject]]). - Return obj.
27.2.4.10 get Promise [ %Symbol.species% ]
Promise[%Symbol.species%] is an
- Return the
this value.
The value of the
Promise prototype methods normally use their
27.2.5 Properties of the Promise Prototype Object
The Promise prototype object:
- is %Promise.prototype%.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a [[PromiseState]] internal slot or any of the other internal slots of Promise instances.
27.2.5.1 Promise.prototype.catch ( onRejected )
This method performs the following steps when called:
- Let promise be the
this value. - Return ?
Invoke (promise,"then" , «undefined , onRejected »).
27.2.5.2 Promise.prototype.constructor
The initial value of Promise.prototype.constructor is
27.2.5.3 Promise.prototype.finally ( onFinally )
This method performs the following steps when called:
- Let promise be the
this value. - If promise
is not an Object , throw aTypeError exception. - Let C be ?
SpeciesConstructor (promise,%Promise% ). Assert :IsConstructor (C) istrue .- If
IsCallable (onFinally) isfalse , then- Let thenFinally be onFinally.
- Let catchFinally be onFinally.
- Else,
- Let thenFinallyClosure be a new
Abstract Closure with parameters (value) that captures onFinally and C and performs the following steps when called:- Let result be ?
Call (onFinally,undefined ). - Let p be ?
PromiseResolve (C, result). - Let returnValue be a new
Abstract Closure with no parameters that captures value and performs the following steps when called:- Return
NormalCompletion (value).
- Return
- Let valueThunk be
CreateBuiltinFunction (returnValue, 0,"" , « »). - Return ?
Invoke (p,"then" , « valueThunk »).
- Let result be ?
- Let thenFinally be
CreateBuiltinFunction (thenFinallyClosure, 1,"" , « »). - Let catchFinallyClosure be a new
Abstract Closure with parameters (reason) that captures onFinally and C and performs the following steps when called:- Let result be ?
Call (onFinally,undefined ). - Let p be ?
PromiseResolve (C, result). - Let throwReason be a new
Abstract Closure with no parameters that captures reason and performs the following steps when called:- Return
ThrowCompletion (reason).
- Return
- Let thrower be
CreateBuiltinFunction (throwReason, 0,"" , « »). - Return ?
Invoke (p,"then" , « thrower »).
- Let result be ?
- Let catchFinally be
CreateBuiltinFunction (catchFinallyClosure, 1,"" , « »).
- Let thenFinallyClosure be a new
- Return ?
Invoke (promise,"then" , « thenFinally, catchFinally »).
27.2.5.4 Promise.prototype.then ( onFulfilled, onRejected )
This method performs the following steps when called:
- Let promise be the
this value. - If
IsPromise (promise) isfalse , throw aTypeError exception. - Let C be ?
SpeciesConstructor (promise,%Promise% ). - Let resultCapability be ?
NewPromiseCapability (C). - Return
PerformPromiseThen (promise, onFulfilled, onRejected, resultCapability).
27.2.5.4.1 PerformPromiseThen ( promise, onFulfilled, onRejected [ , resultCapability ] )
The abstract operation PerformPromiseThen takes arguments promise (a Promise),
onFulfilled (an
Assert :IsPromise (promise) istrue .- If resultCapability is not present, then
- Set resultCapability to
undefined .
- Set resultCapability to
- If
IsCallable (onFulfilled) isfalse , then- Let onFulfilledJobCallback be
empty .
- Let onFulfilledJobCallback be
- Else,
- Let onFulfilledJobCallback be
HostMakeJobCallback (onFulfilled).
- Let onFulfilledJobCallback be
- If
IsCallable (onRejected) isfalse , then- Let onRejectedJobCallback be
empty .
- Let onRejectedJobCallback be
- Else,
- Let onRejectedJobCallback be
HostMakeJobCallback (onRejected).
- Let onRejectedJobCallback be
- Let fulfillReaction be the
PromiseReaction Record { [[Capability]]: resultCapability, [[Type]]:fulfill , [[Handler]]: onFulfilledJobCallback }. - Let rejectReaction be the
PromiseReaction Record { [[Capability]]: resultCapability, [[Type]]:reject , [[Handler]]: onRejectedJobCallback }. - If promise.[[PromiseState]] is
pending , then- Append fulfillReaction to promise.[[PromiseFulfillReactions]].
- Append rejectReaction to promise.[[PromiseRejectReactions]].
- Else if promise.[[PromiseState]] is
fulfilled , then- Let value be promise.[[PromiseResult]].
- Let fulfillJob be
NewPromiseReactionJob (fulfillReaction, value). - Perform
HostEnqueuePromiseJob (fulfillJob.[[Job]], fulfillJob.[[Realm]]).
- Else,
Assert : promise.[[PromiseState]] isrejected .- Let reason be promise.[[PromiseResult]].
- If promise.[[PromiseIsHandled]] is
false , performHostPromiseRejectionTracker (promise,"handle" ). - Let rejectJob be
NewPromiseReactionJob (rejectReaction, reason). - Perform
HostEnqueuePromiseJob (rejectJob.[[Job]], rejectJob.[[Realm]]).
- Set promise.[[PromiseIsHandled]] to
true . - If resultCapability is
undefined , then- Return
undefined .
- Return
- Else,
- Return resultCapability.[[Promise]].
27.2.5.5 Promise.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
27.2.6 Properties of Promise Instances
Promise instances are
| Internal Slot | Type | Description |
|---|---|---|
| [[PromiseState]] |
|
Governs how a promise will react to incoming calls to its then
method.
|
| [[PromiseResult]] |
an |
The value with which the promise has been fulfilled or rejected, if any.
|
| [[PromiseFulfillReactions]] |
a |
|
| [[PromiseRejectReactions]] |
a |
|
| [[PromiseIsHandled]] | a Boolean | Indicates whether the promise has ever had a fulfillment or rejection handler; used in unhandled rejection tracking. |
27.3 GeneratorFunction Objects
GeneratorFunctions are functions that are usually created by evaluating
27.3.1 The GeneratorFunction Constructor
The GeneratorFunction
- is %GeneratorFunction%.
- is a subclass of
Function. - creates and initializes a new GeneratorFunction when called as a function rather than as a
constructor . Thus the function callGeneratorFunction (…)is equivalent to the object creation expressionnew GeneratorFunction (…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified GeneratorFunction behaviour must include asupercall to the GeneratorFunctionconstructor to create and initialize subclass instances with the internal slots necessary for built-in GeneratorFunction behaviour. All ECMAScript syntactic forms for defining generatorfunction objects create direct instances of GeneratorFunction. There is no syntactic means to create instances of GeneratorFunction subclasses.
27.3.1.1 GeneratorFunction ( ...parameterArgs, bodyArg )
The last argument (if any) specifies the body (executable code) of a generator function; any preceding arguments specify formal parameters.
This function performs the following steps when called:
- Let C be the
active function object . - If bodyArg is not present, set bodyArg to the empty String.
- Return ?
CreateDynamicFunction (C, NewTarget,generator , parameterArgs, bodyArg).
See NOTE for
27.3.2 Properties of the GeneratorFunction Constructor
The GeneratorFunction
- is a standard built-in
function object that inherits from the Functionconstructor . - has a [[Prototype]] internal slot whose value is
%Function% . - has a
"length" property whose value is1 𝔽. - has a
"name" property whose value is"GeneratorFunction" . - has the following properties:
27.3.2.1 GeneratorFunction.prototype
The initial value of GeneratorFunction.prototype is the
This property has the attributes { [[Writable]]:
27.3.3 Properties of the GeneratorFunction Prototype Object
The GeneratorFunction prototype object:
- is %GeneratorFunction.prototype% (see
Figure 6 ). - is an
ordinary object . - is not a
function object and does not have an [[ECMAScriptCode]] internal slot or any other of the internal slots listed inTable 30 orTable 93 . - has a [[Prototype]] internal slot whose value is
%Function.prototype% .
27.3.3.1 GeneratorFunction.prototype.constructor
The initial value of GeneratorFunction.prototype.constructor is
This property has the attributes { [[Writable]]:
27.3.3.2 GeneratorFunction.prototype.prototype
The initial value of GeneratorFunction.prototype.prototype is
This property has the attributes { [[Writable]]:
27.3.3.3 GeneratorFunction.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
27.3.4 GeneratorFunction Instances
Every GeneratorFunction instance is an ECMAScript
Each GeneratorFunction instance has the following own properties:
27.3.4.1 length
The specification for the
27.3.4.2 name
The specification for the
27.3.4.3 prototype
Whenever a GeneratorFunction instance is created another
This property has the attributes { [[Writable]]:
Unlike Function instances, the object that is the value of a GeneratorFunction's
27.4 AsyncGeneratorFunction Objects
AsyncGeneratorFunctions are functions that are usually created by evaluating
27.4.1 The AsyncGeneratorFunction Constructor
The AsyncGeneratorFunction
- is %AsyncGeneratorFunction%.
- is a subclass of
Function. - creates and initializes a new AsyncGeneratorFunction when called as a function rather than
as a
constructor . Thus the function callAsyncGeneratorFunction (...)is equivalent to the object creation expressionnew AsyncGeneratorFunction (...)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified AsyncGeneratorFunction behaviour must include asupercall to the AsyncGeneratorFunctionconstructor to create and initialize subclass instances with the internal slots necessary for built-in AsyncGeneratorFunction behaviour. All ECMAScript syntactic forms for defining async generatorfunction objects create direct instances of AsyncGeneratorFunction. There is no syntactic means to create instances of AsyncGeneratorFunction subclasses.
27.4.1.1 AsyncGeneratorFunction ( ...parameterArgs, bodyArg )
The last argument (if any) specifies the body (executable code) of an async generator function; any preceding arguments specify formal parameters.
This function performs the following steps when called:
- Let C be the
active function object . - If bodyArg is not present, set bodyArg to the empty String.
- Return ?
CreateDynamicFunction (C, NewTarget,async-generator , parameterArgs, bodyArg).
See NOTE for
27.4.2 Properties of the AsyncGeneratorFunction Constructor
The AsyncGeneratorFunction
- is a standard built-in
function object that inherits from the Functionconstructor . - has a [[Prototype]] internal slot whose value is
%Function% . - has a
"length" property whose value is1 𝔽. - has a
"name" property whose value is"AsyncGeneratorFunction" . - has the following properties:
27.4.2.1 AsyncGeneratorFunction.prototype
The initial value of AsyncGeneratorFunction.prototype is the
This property has the attributes { [[Writable]]:
27.4.3 Properties of the AsyncGeneratorFunction Prototype Object
The AsyncGeneratorFunction prototype object:
- is %AsyncGeneratorFunction.prototype%.
- is an
ordinary object . - is not a
function object and does not have an [[ECMAScriptCode]] internal slot or any other of the internal slots listed inTable 30 orTable 94 . - has a [[Prototype]] internal slot whose value is
%Function.prototype% .
27.4.3.1 AsyncGeneratorFunction.prototype.constructor
The initial value of AsyncGeneratorFunction.prototype.constructor is
This property has the attributes { [[Writable]]:
27.4.3.2 AsyncGeneratorFunction.prototype.prototype
The initial value of AsyncGeneratorFunction.prototype.prototype is
This property has the attributes { [[Writable]]:
27.4.3.3 AsyncGeneratorFunction.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
27.4.4 AsyncGeneratorFunction Instances
Every AsyncGeneratorFunction instance is an ECMAScript
Each AsyncGeneratorFunction instance has the following own properties:
27.4.4.1 length
The value of the
This property has the attributes { [[Writable]]:
27.4.4.2 name
The specification for the
27.4.4.3 prototype
Whenever an AsyncGeneratorFunction instance is created, another
This property has the attributes { [[Writable]]:
Unlike function instances, the object that is the value of an
AsyncGeneratorFunction's
27.5 Generator Objects
A Generator is created by calling a generator function and conforms to both the
Generator instances directly inherit properties from the initial value of the
27.5.1 The %GeneratorPrototype% Object
The %GeneratorPrototype% object:
- is %GeneratorFunction.prototype.prototype%.
- is an
ordinary object . - is not a Generator instance and does not have a [[GeneratorState]] internal slot.
- has a [[Prototype]] internal slot whose value is
%Iterator.prototype% . - has properties that are indirectly inherited by all Generator instances.
27.5.1.1 %GeneratorPrototype%.constructor
The initial value of .constructor
is
This property has the attributes { [[Writable]]:
27.5.1.2 %GeneratorPrototype%.next ( value )
- Return ?
GeneratorResume (this value, value,empty ).
27.5.1.3 %GeneratorPrototype%.return ( value )
This method performs the following steps when called:
- Let g be the
this value. - Let C be
ReturnCompletion (value). - Return ?
GeneratorResumeAbrupt (g, C,empty ).
27.5.1.4 %GeneratorPrototype%.throw ( exception )
This method performs the following steps when called:
- Let g be the
this value. - Let C be
ThrowCompletion (exception). - Return ?
GeneratorResumeAbrupt (g, C,empty ).
27.5.1.5 %GeneratorPrototype% [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
27.5.2 Properties of Generator Instances
Generator instances are initially created with the internal slots described in
| Internal Slot | Type | Description |
|---|---|---|
| [[GeneratorState]] |
|
The current execution state of the generator. |
| [[GeneratorContext]] |
an |
The |
| [[GeneratorBrand]] |
a String or |
A brand used to distinguish different kinds of generators. The [[GeneratorBrand]] of generators declared by
|
27.5.3 Generator Abstract Operations
27.5.3.1 GeneratorStart ( generator, generatorBody )
The abstract operation GeneratorStart takes arguments generator (a Generator) and
generatorBody (a
Assert : generator.[[GeneratorState]] issuspended-start .- Let genContext be the
running execution context . - Set the Generator component of genContext to generator.
- Let closure be a new
Abstract Closure with no parameters that captures generatorBody and performs the following steps when called:- Let acGenContext be the
running execution context . - Let acGenerator be the Generator component of acGenContext.
- If generatorBody is a
Parse Node , then- Let result be
Completion (Evaluation of generatorBody).
- Let result be
- Else,
Assert : generatorBody is anAbstract Closure with no parameters.- Let result be
Completion (generatorBody()).
Assert : If we return here, the generator either threw an exception or performed either an implicit or explicit return.- Remove acGenContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - Set acGenerator.[[GeneratorState]] to
completed . - NOTE: Once a generator enters the
completed state it never leaves it and its associatedexecution context is never resumed. Any execution state associated with acGenerator can be discarded at this point. - If result is a
normal completion , then- Let resultValue be
undefined .
- Let resultValue be
- Else if result is a
return completion , then- Let resultValue be result.[[Value]].
- Else,
Assert : result is athrow completion .- Return ? result.
- Return
NormalCompletion (CreateIteratorResultObject (resultValue,true )).
- Let acGenContext be the
- Set the code evaluation state of genContext such that when evaluation is
resumed for that
execution context , closure will be called with no arguments. - Set generator.[[GeneratorContext]] to genContext.
- Return
unused .
27.5.3.2 GeneratorValidate ( generator, generatorBrand )
The abstract operation GeneratorValidate takes arguments generator (an
- Perform ?
RequireInternalSlot (generator, [[GeneratorState]]). - Perform ?
RequireInternalSlot (generator, [[GeneratorBrand]]). - If generator.[[GeneratorBrand]] is not
generatorBrand, throw a
TypeError exception. Assert : generator also has a [[GeneratorContext]] internal slot.- Let state be generator.[[GeneratorState]].
- If state is
executing , throw aTypeError exception. - Return state.
27.5.3.3 GeneratorResume ( generator, value, generatorBrand )
The abstract operation GeneratorResume takes arguments generator (an
- Let state be ?
GeneratorValidate (generator, generatorBrand). - If state is
completed , returnCreateIteratorResultObject (undefined ,true ). Assert : state is eithersuspended-start orsuspended-yield .- Let genContext be generator.[[GeneratorContext]].
- Let methodContext be the
running execution context . - Suspend methodContext.
- Set generator.[[GeneratorState]] to
executing . - Push genContext onto the
execution context stack ; genContext is now therunning execution context . - Resume the suspended evaluation of
genContext using
NormalCompletion (value) as the result of the operation that suspended it. Let result be the value returned by the resumed computation. Assert : When we return here, genContext has already been removed from theexecution context stack and methodContext is the currentlyrunning execution context .- Return ? result.
27.5.3.4 GeneratorResumeAbrupt ( generator, abruptCompletion, generatorBrand )
The abstract operation GeneratorResumeAbrupt takes arguments generator (an
- Let state be ?
GeneratorValidate (generator, generatorBrand). - If state is
suspended-start , then- Set generator.[[GeneratorState]] to
completed . - NOTE: Once a generator enters the
completed state it never leaves it and its associatedexecution context is never resumed. Any execution state associated with generator can be discarded at this point. - Set state to
completed .
- Set generator.[[GeneratorState]] to
- If state is
completed , then- If abruptCompletion is a
return completion , then- Return
CreateIteratorResultObject (abruptCompletion.[[Value]],true ).
- Return
- Return ? abruptCompletion.
- If abruptCompletion is a
Assert : state issuspended-yield .- Let genContext be generator.[[GeneratorContext]].
- Let methodContext be the
running execution context . - Suspend methodContext.
- Set generator.[[GeneratorState]] to
executing . - Push genContext onto the
execution context stack ; genContext is now therunning execution context . - Resume the suspended evaluation of
genContext using abruptCompletion as the result of
the operation that suspended it. Let result be the
Completion Record returned by the resumed computation. Assert : When we return here, genContext has already been removed from theexecution context stack and methodContext is the currentlyrunning execution context .- Return ? result.
27.5.3.5 GetGeneratorKind ( )
The abstract operation GetGeneratorKind takes no arguments and returns
- Let genContext be the
running execution context . - If genContext does not have a Generator component, return
non-generator . - Let generator be the Generator component of genContext.
- If generator has an [[AsyncGeneratorState]]
internal slot, return
async . - Else, return
sync .
27.5.3.6 GeneratorYield ( iteratorResult )
The abstract operation GeneratorYield takes argument iteratorResult (an Object
that conforms to the
- Let genContext be the
running execution context . Assert : genContext is theexecution context of a generator.- Let generator be the value of the Generator component of genContext.
Assert :GetGeneratorKind () issync .- Set generator.[[GeneratorState]] to
suspended-yield . - Remove genContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - Let callerContext be the
running execution context . - Resume callerContext passing
NormalCompletion (iteratorResult). If genContext is ever resumed again, let resumptionValue be theCompletion Record with which it is resumed. Assert : If control reaches here, then genContext is therunning execution context again.- Return resumptionValue.
27.5.3.7 Yield ( value )
The abstract operation Yield takes argument value (an
- Let generatorKind be
GetGeneratorKind (). - If generatorKind is
async , return ?AsyncGeneratorYield (?Await (value)). - Otherwise, return ?
GeneratorYield (CreateIteratorResultObject (value,false )).
27.5.3.8 CreateIteratorFromClosure ( closure, generatorBrand, generatorPrototype [ , extraSlots ] )
The abstract operation CreateIteratorFromClosure takes arguments closure (an
- NOTE: closure can contain uses of the
Yield operation to yield anIteratorResult object . - If extraSlots is not present, set extraSlots to a new empty
List . - Let internalSlotsList be the
list-concatenation of extraSlots and « [[GeneratorState]], [[GeneratorContext]], [[GeneratorBrand]] ». - Let generator be
OrdinaryObjectCreate (generatorPrototype, internalSlotsList). - Set generator.[[GeneratorBrand]] to generatorBrand.
- Set generator.[[GeneratorState]] to
suspended-start . - Let callerContext be the
running execution context . - Let calleeContext be a new
execution context . - Set the Function of calleeContext to
null . - Set the
Realm of calleeContext tothe current Realm Record . - Set the ScriptOrModule of calleeContext to callerContext's ScriptOrModule.
- If callerContext is not already suspended, suspend callerContext.
- Push calleeContext onto the
execution context stack ; calleeContext is now therunning execution context . - Perform
GeneratorStart (generator, closure). - Remove calleeContext from the
execution context stack and restore callerContext as therunning execution context . - Return generator.
27.6 AsyncGenerator Objects
An AsyncGenerator is created by calling an async generator function and conforms to both the
AsyncGenerator instances directly inherit properties from the initial value of the
27.6.1 The %AsyncGeneratorPrototype% Object
The %AsyncGeneratorPrototype% object:
- is %AsyncGeneratorFunction.prototype.prototype%.
- is an
ordinary object . - is not an AsyncGenerator instance and does not have an [[AsyncGeneratorState]] internal slot.
- has a [[Prototype]] internal slot whose value is
%AsyncIteratorPrototype% . - has properties that are indirectly inherited by all AsyncGenerator instances.
27.6.1.1 %AsyncGeneratorPrototype%.constructor
The initial value of .constructor
is
This property has the attributes { [[Writable]]:
27.6.1.2 %AsyncGeneratorPrototype%.next ( value )
- Let generator be the
this value. - Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let result be
Completion (AsyncGeneratorValidate (generator,empty )). IfAbruptRejectPromise (result, promiseCapability).- Let state be generator.[[AsyncGeneratorState]].
- If state is
completed , then- Let iteratorResult be
CreateIteratorResultObject (undefined ,true ). - Perform ! Call(promiseCapability.[[Resolve]],
undefined , « iteratorResult »). - Return promiseCapability.[[Promise]].
- Let iteratorResult be
- Let completion be
NormalCompletion (value). - Perform
AsyncGeneratorEnqueue (generator, completion, promiseCapability). - If state is either
suspended-start orsuspended-yield , then- Perform
AsyncGeneratorResume (generator, completion).
- Perform
- Else,
Assert : state is eitherexecuting ordraining-queue .
- Return promiseCapability.[[Promise]].
27.6.1.3 %AsyncGeneratorPrototype%.return ( value )
- Let generator be the
this value. - Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let result be
Completion (AsyncGeneratorValidate (generator,empty )). IfAbruptRejectPromise (result, promiseCapability).- Let completion be
ReturnCompletion (value). - Perform
AsyncGeneratorEnqueue (generator, completion, promiseCapability). - Let state be generator.[[AsyncGeneratorState]].
- If state is either
suspended-start orcompleted , then- Set generator.[[AsyncGeneratorState]] to
draining-queue . - Perform
AsyncGeneratorAwaitReturn (generator).
- Set generator.[[AsyncGeneratorState]] to
- Else if state is
suspended-yield , then- Perform
AsyncGeneratorResume (generator, completion).
- Perform
- Else,
Assert : state is eitherexecuting ordraining-queue .
- Return promiseCapability.[[Promise]].
27.6.1.4 %AsyncGeneratorPrototype%.throw ( exception )
- Let generator be the
this value. - Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let result be
Completion (AsyncGeneratorValidate (generator,empty )). IfAbruptRejectPromise (result, promiseCapability).- Let state be generator.[[AsyncGeneratorState]].
- If state is
suspended-start , then- Set generator.[[AsyncGeneratorState]] to
completed . - Set state to
completed .
- Set generator.[[AsyncGeneratorState]] to
- If state is
completed , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « exception »). - Return promiseCapability.[[Promise]].
- Perform !
- Let completion be
ThrowCompletion (exception). - Perform
AsyncGeneratorEnqueue (generator, completion, promiseCapability). - If state is
suspended-yield , then- Perform
AsyncGeneratorResume (generator, completion).
- Perform
- Else,
Assert : state is eitherexecuting ordraining-queue .
- Return promiseCapability.[[Promise]].
27.6.1.5 %AsyncGeneratorPrototype% [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
27.6.2 Properties of AsyncGenerator Instances
AsyncGenerator instances are initially created with the internal slots described below:
| Internal Slot | Type | Description |
|---|---|---|
| [[AsyncGeneratorState]] | The current execution state of the async generator. | |
| [[AsyncGeneratorContext]] | an |
The |
| [[AsyncGeneratorQueue]] | a |
|
| [[GeneratorBrand]] | a String or |
A brand used to distinguish different kinds of async generators. The [[GeneratorBrand]] of async generators declared by
|
27.6.3 AsyncGenerator Abstract Operations
27.6.3.1 AsyncGeneratorRequest Records
An AsyncGeneratorRequest is a
They have the following fields:
| Field Name | Value | Meaning |
|---|---|---|
| [[Completion]] | a |
The |
| [[Capability]] | a |
The promise capabilities associated with this request. |
27.6.3.2 AsyncGeneratorStart ( generator, generatorBody )
The abstract operation AsyncGeneratorStart takes arguments generator (an
AsyncGenerator) and generatorBody (a
Assert : generator.[[AsyncGeneratorState]] issuspended-start .- Let genContext be the
running execution context . - Set the Generator component of genContext to generator.
- Let closure be a new
Abstract Closure with no parameters that captures generatorBody and performs the following steps when called:- Let acGenContext be the
running execution context . - Let acGenerator be the Generator component of acGenContext.
- If generatorBody is a
Parse Node , then- Let result be
Completion (Evaluation of generatorBody).
- Let result be
- Else,
Assert : generatorBody is anAbstract Closure with no parameters.- Let result be
Completion (generatorBody()).
Assert : If we return here, the async generator either threw an exception or performed either an implicit or explicit return.- Remove acGenContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - Set acGenerator.[[AsyncGeneratorState]]
to
draining-queue . - If result is a
normal completion , set result toNormalCompletion (undefined ). - If result is a
return completion , set result toNormalCompletion (result.[[Value]]). - Perform
AsyncGeneratorCompleteStep (acGenerator, result,true ). - Perform
AsyncGeneratorDrainQueue (acGenerator). - Return
NormalCompletion (undefined ).
- Let acGenContext be the
- Set the code evaluation state of genContext such that when evaluation is
resumed for that
execution context , closure will be called with no arguments. - Set generator.[[AsyncGeneratorContext]] to genContext.
- Set generator.[[AsyncGeneratorQueue]] to a new
empty
List . - Return
unused .
27.6.3.3 AsyncGeneratorValidate ( generator, generatorBrand )
The abstract operation AsyncGeneratorValidate takes arguments generator (an
- Perform ?
RequireInternalSlot (generator, [[AsyncGeneratorContext]]). - Perform ?
RequireInternalSlot (generator, [[AsyncGeneratorState]]). - Perform ?
RequireInternalSlot (generator, [[AsyncGeneratorQueue]]). - If generator.[[GeneratorBrand]] is not
generatorBrand, throw a
TypeError exception. - Return
unused .
27.6.3.4 AsyncGeneratorEnqueue ( generator, completion, promiseCapability )
The abstract operation AsyncGeneratorEnqueue takes arguments generator (an
AsyncGenerator), completion (a
- Let request be
AsyncGeneratorRequest { [[Completion]]: completion, [[Capability]]: promiseCapability }. - Append request to generator.[[AsyncGeneratorQueue]].
- Return
unused .
27.6.3.5 AsyncGeneratorCompleteStep ( generator, completion, done [ , realm ] )
The abstract operation AsyncGeneratorCompleteStep takes arguments generator (an
AsyncGenerator), completion (a
Assert : generator.[[AsyncGeneratorQueue]] is not empty.- Let next be the first element of generator.[[AsyncGeneratorQueue]].
- Remove the first element from generator.[[AsyncGeneratorQueue]].
- Let promiseCapability be next.[[Capability]].
- Let value be completion.[[Value]].
- If completion is a
throw completion , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « value »).
- Perform !
- Else,
Assert : completion is anormal completion .- If realm is present, then
- Let oldRealm be the
running execution context 'sRealm . - Set the
running execution context 'sRealm to realm. - Let iteratorResult be
CreateIteratorResultObject (value, done). - Set the
running execution context 'sRealm to oldRealm.
- Let oldRealm be the
- Else,
- Let iteratorResult be
CreateIteratorResultObject (value, done).
- Let iteratorResult be
- Perform ! Call(promiseCapability.[[Resolve]],
undefined , « iteratorResult »).
- Return
unused .
27.6.3.6 AsyncGeneratorResume ( generator, completion )
The abstract operation AsyncGeneratorResume takes arguments generator (an
AsyncGenerator) and completion (a
Assert : generator.[[AsyncGeneratorState]] is eithersuspended-start orsuspended-yield .- Let genContext be generator.[[AsyncGeneratorContext]].
- Let callerContext be the
running execution context . - Suspend callerContext.
- Set generator.[[AsyncGeneratorState]] to
executing . - Push genContext onto the
execution context stack ; genContext is now therunning execution context . - Resume the suspended evaluation of
genContext using completion as the result of the
operation that suspended it. Let result be the
Completion Record returned by the resumed computation. Assert : result is never anabrupt completion .Assert : When we return here, genContext has already been removed from theexecution context stack and callerContext is the currentlyrunning execution context .- Return
unused .
27.6.3.7 AsyncGeneratorUnwrapYieldResumption ( resumptionValue )
The abstract operation AsyncGeneratorUnwrapYieldResumption takes argument
resumptionValue (a
- If resumptionValue is not a
return completion , return ? resumptionValue. - Let awaited be
Completion (Await (resumptionValue.[[Value]])). - If awaited is a
throw completion , return ? awaited. Assert : awaited is anormal completion .- Return
ReturnCompletion (awaited.[[Value]]).
27.6.3.8 AsyncGeneratorYield ( value )
The abstract operation AsyncGeneratorYield takes argument value (an
- Let genContext be the
running execution context . Assert : genContext is theexecution context of a generator.- Let generator be the value of the Generator component of genContext.
Assert :GetGeneratorKind () isasync .- Let completion be
NormalCompletion (value). Assert : Theexecution context stack has at least two elements.- Let previousContext be the second to top element of the
execution context stack . - Let previousRealm be previousContext's
Realm . - Perform
AsyncGeneratorCompleteStep (generator, completion,false , previousRealm). - Let queue be generator.[[AsyncGeneratorQueue]].
- If queue is not empty, then
- NOTE: Execution continues without suspending the generator.
- Let toYield be the first element of queue.
- Let resumptionValue be
Completion (toYield.[[Completion]]). - Return ?
AsyncGeneratorUnwrapYieldResumption (resumptionValue).
- Else,
- Set generator.[[AsyncGeneratorState]] to
suspended-yield . - Remove genContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - Let callerContext be the
running execution context . - Resume callerContext passing
undefined . If genContext is ever resumed again, let resumptionValue be theCompletion Record with which it is resumed. Assert : If control reaches here, then genContext is therunning execution context again.- Return ?
AsyncGeneratorUnwrapYieldResumption (resumptionValue).
- Set generator.[[AsyncGeneratorState]] to
27.6.3.9 AsyncGeneratorAwaitReturn ( generator )
The abstract operation AsyncGeneratorAwaitReturn takes argument generator (an
AsyncGenerator) and returns
Assert : generator.[[AsyncGeneratorState]] isdraining-queue .- Let queue be generator.[[AsyncGeneratorQueue]].
Assert : queue is not empty.- Let next be the first element of queue.
- Let completion be
Completion (next.[[Completion]]). Assert : completion is areturn completion .- Let promiseCompletion be
Completion (PromiseResolve (%Promise% , completion.[[Value]])). - If promiseCompletion is an
abrupt completion , then- Perform
AsyncGeneratorCompleteStep (generator, promiseCompletion,true ). - Perform
AsyncGeneratorDrainQueue (generator). - Return
unused .
- Perform
Assert : promiseCompletion is anormal completion .- Let promise be promiseCompletion.[[Value]].
- Let fulfilledClosure be a new
Abstract Closure with parameters (value) that captures generator and performs the following steps when called:Assert : generator.[[AsyncGeneratorState]] isdraining-queue .- Let result be
NormalCompletion (value). - Perform
AsyncGeneratorCompleteStep (generator, result,true ). - Perform
AsyncGeneratorDrainQueue (generator). - Return
NormalCompletion (undefined ).
- Let onFulfilled be
CreateBuiltinFunction (fulfilledClosure, 1,"" , « »). - Let rejectedClosure be a new
Abstract Closure with parameters (reason) that captures generator and performs the following steps when called:Assert : generator.[[AsyncGeneratorState]] isdraining-queue .- Let result be
ThrowCompletion (reason). - Perform
AsyncGeneratorCompleteStep (generator, result,true ). - Perform
AsyncGeneratorDrainQueue (generator). - Return
NormalCompletion (undefined ).
- Let onRejected be
CreateBuiltinFunction (rejectedClosure, 1,"" , « »). - Perform
PerformPromiseThen (promise, onFulfilled, onRejected). - Return
unused .
27.6.3.10 AsyncGeneratorDrainQueue ( generator )
The abstract operation AsyncGeneratorDrainQueue takes argument generator (an
AsyncGenerator) and returns
Assert : generator.[[AsyncGeneratorState]] isdraining-queue .- Let queue be generator.[[AsyncGeneratorQueue]].
- Repeat, while queue is not empty,
- Let next be the first element of queue.
- Let completion be
Completion (next.[[Completion]]). - If completion is a
return completion , then- Perform
AsyncGeneratorAwaitReturn (generator). - Return
unused .
- Perform
- Else,
- If completion is a
normal completion , then- Set completion to
NormalCompletion (undefined ).
- Set completion to
- Perform
AsyncGeneratorCompleteStep (generator, completion,true ).
- If completion is a
- Set generator.[[AsyncGeneratorState]] to
completed . - Return
unused .
27.6.3.11 CreateAsyncIteratorFromClosure ( closure, generatorBrand, generatorPrototype )
The abstract operation CreateAsyncIteratorFromClosure takes arguments closure (an
- NOTE: closure can contain uses of the
Await operation and uses of theYield operation to yield anIteratorResult object . - Let internalSlotsList be « [[AsyncGeneratorState]], [[AsyncGeneratorContext]], [[AsyncGeneratorQueue]], [[GeneratorBrand]] ».
- Let generator be
OrdinaryObjectCreate (generatorPrototype, internalSlotsList). - Set generator.[[GeneratorBrand]] to generatorBrand.
- Set generator.[[AsyncGeneratorState]] to
suspended-start . - Let callerContext be the
running execution context . - Let calleeContext be a new
execution context . - Set the Function of calleeContext to
null . - Set the
Realm of calleeContext tothe current Realm Record . - Set the ScriptOrModule of calleeContext to callerContext's ScriptOrModule.
- If callerContext is not already suspended, suspend callerContext.
- Push calleeContext onto the
execution context stack ; calleeContext is now therunning execution context . - Perform
AsyncGeneratorStart (generator, closure). - Remove calleeContext from the
execution context stack and restore callerContext as therunning execution context . - Return generator.
27.7 AsyncFunction Objects
AsyncFunctions are functions that are usually created by evaluating
27.7.1 The AsyncFunction Constructor
The AsyncFunction
- is %AsyncFunction%.
- is a subclass of
Function. - creates and initializes a new AsyncFunction when called as a function rather than as a
constructor . Thus the function callAsyncFunction(…)is equivalent to the object creation expressionnew AsyncFunction(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified AsyncFunction behaviour must include asupercall to the AsyncFunctionconstructor to create and initialize a subclass instance with the internal slots necessary for built-in async function behaviour. All ECMAScript syntactic forms for defining asyncfunction objects create direct instances of AsyncFunction. There is no syntactic means to create instances of AsyncFunction subclasses.
27.7.1.1 AsyncFunction ( ...parameterArgs, bodyArg )
The last argument (if any) specifies the body (executable code) of an async function. Any preceding arguments specify formal parameters.
This function performs the following steps when called:
- Let C be the
active function object . - If bodyArg is not present, set bodyArg to the empty String.
- Return ?
CreateDynamicFunction (C, NewTarget,async , parameterArgs, bodyArg).
27.7.2 Properties of the AsyncFunction Constructor
The AsyncFunction
- is a standard built-in
function object that inherits from the Functionconstructor . - has a [[Prototype]] internal slot whose value is
%Function% . - has a
"length" property whose value is1 𝔽. - has a
"name" property whose value is"AsyncFunction" . - has the following properties:
27.7.2.1 AsyncFunction.prototype
The initial value of AsyncFunction.prototype is the
This property has the attributes { [[Writable]]:
27.7.3 Properties of the AsyncFunction Prototype Object
The AsyncFunction prototype object:
- is %AsyncFunction.prototype%.
- is an
ordinary object . - is not a
function object and does not have an [[ECMAScriptCode]] internal slot or any other of the internal slots listed inTable 30 . - has a [[Prototype]] internal slot whose value is
%Function.prototype% .
27.7.3.1 AsyncFunction.prototype.constructor
The initial value of AsyncFunction.prototype.constructor is
This property has the attributes { [[Writable]]:
27.7.3.2 AsyncFunction.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
27.7.4 AsyncFunction Instances
Every AsyncFunction instance is an ECMAScript
Each AsyncFunction instance has the following own properties:
27.7.4.1 length
The specification for the
27.7.4.2 name
The specification for the
27.7.5 Async Functions Abstract Operations
27.7.5.1 AsyncFunctionStart ( promiseCapability, asyncFunctionBody )
The abstract operation AsyncFunctionStart takes arguments promiseCapability (a
- Let runningContext be the
running execution context . - Let asyncContext be a copy of runningContext.
- NOTE: Copying the execution state is required for
AsyncBlockStart to resume its execution. It is ill-defined to resume a currently executing context. - Perform
AsyncBlockStart (promiseCapability, asyncFunctionBody, asyncContext). - Return
unused .
27.7.5.2 AsyncBlockStart ( promiseCapability, asyncBody, asyncContext )
The abstract operation AsyncBlockStart takes arguments promiseCapability (a
- Let runningContext be the
running execution context . - Let closure be a new
Abstract Closure with no parameters that captures promiseCapability and asyncBody and performs the following steps when called:- Let acAsyncContext be the
running execution context . - If asyncBody is a
Parse Node , then- Let result be
Completion (Evaluation of asyncBody).
- Let result be
- Else,
Assert : asyncBody is anAbstract Closure with no parameters.- Let result be
Completion (asyncBody()).
Assert : If we return here, the async function either threw an exception or performed an implicit or explicit return; all awaiting is done.- Remove acAsyncContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - If result is a
normal completion , then- Perform !
Call (promiseCapability.[[Resolve]],undefined , «undefined »).
- Perform !
- Else if result is a
return completion , then- Perform ! Call(promiseCapability.[[Resolve]],
undefined , « result.[[Value]] »).
- Perform ! Call(promiseCapability.[[Resolve]],
- Else,
Assert : result is athrow completion .- Perform !
Call (promiseCapability.[[Reject]],undefined , « result.[[Value]] »).
- Return
NormalCompletion (unused ).
- Let acAsyncContext be the
- Set the code evaluation state of asyncContext such that when evaluation
is resumed for that
execution context , closure will be called with no arguments. - Push asyncContext onto the
execution context stack ; asyncContext is now therunning execution context . - Resume the suspended evaluation of asyncContext. Let result be the value returned by the resumed computation.
Assert : When we return here, asyncContext has already been removed from theexecution context stack and runningContext is the currentlyrunning execution context .Assert : result is anormal completion with a value ofunused . The possible sources of this value areAwait or, if the async function doesn't await anything, step2.i above.- Return
unused .
27.7.5.3 Await ( value )
The abstract operation Await takes argument value (an
- Let asyncContext be the
running execution context . - Let promise be ?
PromiseResolve (%Promise% , value). - Let fulfilledClosure be a new
Abstract Closure with parameters (v) that captures asyncContext and performs the following steps when called:- Let prevContext be the
running execution context . - Suspend prevContext.
- Push asyncContext onto the
execution context stack ; asyncContext is now therunning execution context . - Resume the suspended evaluation of
asyncContext using
NormalCompletion (v) as the result of the operation that suspended it. Assert : When we reach this step, asyncContext has already been removed from theexecution context stack and prevContext is the currentlyrunning execution context .- Return
NormalCompletion (undefined ).
- Let prevContext be the
- Let onFulfilled be
CreateBuiltinFunction (fulfilledClosure, 1,"" , « »). - Let rejectedClosure be a new
Abstract Closure with parameters (reason) that captures asyncContext and performs the following steps when called:- Let prevContext be the
running execution context . - Suspend prevContext.
- Push asyncContext onto the
execution context stack ; asyncContext is now therunning execution context . - Resume the suspended evaluation of
asyncContext using
ThrowCompletion (reason) as the result of the operation that suspended it. Assert : When we reach this step, asyncContext has already been removed from theexecution context stack and prevContext is the currentlyrunning execution context .- Return
NormalCompletion (undefined ).
- Let prevContext be the
- Let onRejected be
CreateBuiltinFunction (rejectedClosure, 1,"" , « »). - Perform
PerformPromiseThen (promise, onFulfilled, onRejected). - Remove asyncContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - Let callerContext be the
running execution context . - Resume callerContext passing
empty . If asyncContext is ever resumed again, let completion be theCompletion Record with which it is resumed. Assert : If control reaches here, then asyncContext is therunning execution context again.- Return completion.
28 Reflection
28.1 The Reflect Object
The Reflect object:
- is %Reflect%.
- is the initial value of the
"Reflect" property of theglobal object . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is not a
function object . - does not have a [[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a [[Call]] internal method; it cannot be invoked as a function.
28.1.1 Reflect.apply ( target, thisArgument, argumentsList )
This function performs the following steps when called:
- If
IsCallable (target) isfalse , throw aTypeError exception. - Let args be ?
CreateListFromArrayLike (argumentsList). - Perform
PrepareForTailCall (). - Return ?
Call (target, thisArgument, args).
28.1.2 Reflect.construct ( target, argumentsList [ , newTarget ] )
This function performs the following steps when called:
- If
IsConstructor (target) isfalse , throw aTypeError exception. - If newTarget is not present, set newTarget to target.
- Else if
IsConstructor (newTarget) isfalse , throw aTypeError exception. - Let args be ?
CreateListFromArrayLike (argumentsList). - Return ?
Construct (target, args, newTarget).
28.1.3 Reflect.defineProperty ( target, propertyKey, attributes )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Let key be ?
ToPropertyKey (propertyKey). - Let desc be ?
ToPropertyDescriptor (attributes). - Return ? target.[[DefineOwnProperty]](key, desc).
28.1.4 Reflect.deleteProperty ( target, propertyKey )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Let key be ?
ToPropertyKey (propertyKey). - Return ? target.[[Delete]](key).
28.1.5 Reflect.get ( target, propertyKey [ , receiver ] )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Let key be ?
ToPropertyKey (propertyKey). - If receiver is not present, then
- Set receiver to target.
- Return ? target.[[Get]](key, receiver).
28.1.6 Reflect.getOwnPropertyDescriptor ( target, propertyKey )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Let key be ?
ToPropertyKey (propertyKey). - Let desc be ? target.[[GetOwnProperty]](key).
- Return
FromPropertyDescriptor (desc).
28.1.7 Reflect.getPrototypeOf ( target )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Return ? target.[[GetPrototypeOf]]().
28.1.8 Reflect.has ( target, propertyKey )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Let key be ?
ToPropertyKey (propertyKey). - Return ? target.[[HasProperty]](key).
28.1.9 Reflect.isExtensible ( target )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Return ? target.[[IsExtensible]]().
28.1.10 Reflect.ownKeys ( target )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Let keys be ? target.[[OwnPropertyKeys]]().
- Return
CreateArrayFromList (keys).
28.1.11 Reflect.preventExtensions ( target )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Return ? target.[[PreventExtensions]]().
28.1.12 Reflect.set ( target, propertyKey, V [ , receiver ] )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - Let key be ?
ToPropertyKey (propertyKey). - If receiver is not present, then
- Set receiver to target.
- Return ? target.[[Set]](key, V, receiver).
28.1.13 Reflect.setPrototypeOf ( target, proto )
This function performs the following steps when called:
- If target
is not an Object , throw aTypeError exception. - If proto
is not an Object and proto is notnull , throw aTypeError exception. - Return ? target.[[SetPrototypeOf]](proto).
28.1.14 Reflect [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
28.2 Proxy Objects
28.2.1 The Proxy Constructor
The Proxy
- is %Proxy%.
- is the initial value of the
"Proxy" property of theglobal object . - creates and initializes a new Proxy object when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
28.2.1.1 Proxy ( target, handler )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Return ?
ProxyCreate (target, handler).
28.2.2 Properties of the Proxy Constructor
The Proxy
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - does not have a
"prototype" property because Proxy objects do not have a [[Prototype]] internal slot that requires initialization. - has the following properties:
28.2.2.1 Proxy.revocable ( target, handler )
This function creates a revocable Proxy object.
It performs the following steps when called:
- Let proxy be ?
ProxyCreate (target, handler). - Let revokerClosure be a new
Abstract Closure with no parameters that captures nothing and performs the following steps when called:- Let F be the
active function object . - Let p be F.[[RevocableProxy]].
- If p is
null , returnNormalCompletion (undefined ). - Set F.[[RevocableProxy]] to
null . Assert : p is aProxy exotic object .- Set p.[[ProxyTarget]] to
null . - Set p.[[ProxyHandler]] to
null . - Return
NormalCompletion (undefined ).
- Let F be the
- Let revoker be
CreateBuiltinFunction (revokerClosure, 0,"" , « [[RevocableProxy]] »). - Set revoker.[[RevocableProxy]] to proxy.
- Let result be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (result,"proxy" , proxy). - Perform !
CreateDataPropertyOrThrow (result,"revoke" , revoker). - Return result.
28.3 Module Namespace Objects
A Module Namespace Object is a
In addition to the properties specified in
28.3.1 %Symbol.toStringTag%
The initial value of the
This property has the attributes { [[Writable]]:
29 Memory Model
The memory consistency model, or memory model, specifies the possible orderings
of
The memory model is defined as relational constraints on events introduced by
This section provides an axiomatic model on events introduced by the
29.1 Memory Model Fundamentals
Shared memory accesses (reads and writes) are divided into two groups, atomic accesses and data
accesses, defined below. Atomic accesses are sequentially consistent, i.e., there is a strict total
ordering of events agreed upon by all
No orderings weaker than sequentially consistent and stronger than unordered, such as release-acquire, are supported.
A Shared Data Block event is either a
ReadSharedMemory, WriteSharedMemory, or ReadModifyWriteSharedMemory
| Field Name | Value | Meaning |
|---|---|---|
| [[Order]] | The weakest ordering guaranteed by the |
|
| [[NoTear]] | a Boolean | Whether this event is allowed to read from multiple write events with equal range as this event. |
| [[Block]] | a |
The block the event operates on. |
| [[ByteIndex]] | a non-negative |
The byte address of the read in [[Block]]. |
| [[ElementSize]] | a non-negative |
The size of the read. |
| Field Name | Value | Meaning |
|---|---|---|
| [[Order]] | The weakest ordering guaranteed by the |
|
| [[NoTear]] | a Boolean | Whether this event is allowed to be read from multiple read events with equal range as this event. |
| [[Block]] | a |
The block the event operates on. |
| [[ByteIndex]] | a non-negative |
The byte address of the write in [[Block]]. |
| [[ElementSize]] | a non-negative |
The size of the write. |
| [[Payload]] | a |
The |
| Field Name | Value | Meaning |
|---|---|---|
| [[Order]] | Read-modify-write events are always sequentially consistent. | |
| [[NoTear]] | Read-modify-write events cannot tear. | |
| [[Block]] | a |
The block the event operates on. |
| [[ByteIndex]] | a non-negative |
The byte address of the read-modify-write in [[Block]]. |
| [[ElementSize]] | a non-negative |
The size of the read-modify-write. |
| [[Payload]] | a |
The |
| [[ModifyOp]] | a |
An abstract closure that returns a modified |
These events are introduced by
Some operations may also introduce Synchronize events. A Synchronize event has no fields, and exists purely to directly constrain the permitted orderings of other events.
In addition to
Let the range of a ReadSharedMemory, WriteSharedMemory, or ReadModifyWriteSharedMemory event be the
Set of contiguous
Examples of postMessage in a browser), starting and stopping
Events are ordered within
29.2 Agent Events Records
An Agent Events Record is a
| Field Name | Value | Meaning |
|---|---|---|
| [[AgentSignifier]] | an |
The |
| [[EventList]] | a |
Events are appended to the list during evaluation. |
| [[AgentSynchronizesWith]] | a |
29.3 Chosen Value Records
A Chosen Value Record is a
| Field Name | Value | Meaning |
|---|---|---|
| [[Event]] | a |
The |
| [[ChosenValue]] | a |
The bytes that were nondeterministically chosen during evaluation. |
29.4 Candidate Executions
A candidate execution of the evaluation of
an
| Field Name | Value | Meaning |
|---|---|---|
| [[EventsRecords]] | a |
Maps an |
| [[ChosenValues]] | a |
Maps |
An empty candidate execution is a
candidate execution
29.5 Abstract Operations for the Memory Model
29.5.1 EventSet ( execution )
The abstract operation EventSet takes argument execution (a
- Let events be an empty Set.
- For each
Agent Events Record aer of execution.[[EventsRecords]], do- For each event E of aer.[[EventList]], do
- Add E to events.
- For each event E of aer.[[EventList]], do
- Return events.
29.5.2 SharedDataBlockEventSet ( execution )
The abstract operation SharedDataBlockEventSet takes argument execution (a
- Let events be an empty Set.
- For each event E of
EventSet (execution), do- If E is a
ReadSharedMemory ,WriteSharedMemory , orReadModifyWriteSharedMemory event, add E to events.
- If E is a
- Return events.
29.5.3 HostEventSet ( execution )
The abstract operation HostEventSet takes argument execution (a
- Let events be an empty Set.
- For each event E of
EventSet (execution), do- If E is not in
SharedDataBlockEventSet (execution), add E to events.
- If E is not in
- Return events.
29.5.4 ComposeWriteEventBytes ( execution, byteIndex, Ws )
The abstract operation ComposeWriteEventBytes takes arguments execution (a
- Let byteLocation be byteIndex.
- Let bytesRead be a new empty
List . - For each element W of Ws, do
Assert : W has byteLocation in its range.- Let payloadIndex be byteLocation - W.[[ByteIndex]].
- If W is a
WriteSharedMemory event, then- Let byte be W.[[Payload]][payloadIndex].
- Else,
Assert : W is aReadModifyWriteSharedMemory event.- Let bytes be
ValueOfReadEvent (execution, W). - Let bytesModified be W.[[ModifyOp]](bytes, W.[[Payload]]).
- Let byte be bytesModified[payloadIndex].
- Append byte to bytesRead.
- Set byteLocation to byteLocation + 1.
- Return bytesRead.
The read-modify-write modification [[ModifyOp]] is given by the
function properties on the Atomics object that introduce
This abstract operation composes a
29.5.5 ValueOfReadEvent ( execution, R )
The abstract operation ValueOfReadEvent takes arguments execution (a
- Let Ws be
reads-bytes-from (R) in execution. Assert : Ws is aList ofWriteSharedMemory orReadModifyWriteSharedMemory events with length equal to R.[[ElementSize]].- Return
ComposeWriteEventBytes (execution, R.[[ByteIndex]], Ws).
29.6 Relations of Candidate Executions
The following relations and mathematical functions are parameterized over a particular
29.6.1 is-agent-order-before
For a
- For events E and D, E is-agent-order-before D in
execution if there is some
Agent Events Record aer in execution.[[EventsRecords]] such that aer.[[EventList]] contains both E and D and E is before D inList order of aer.[[EventList]].
Each
29.6.2 reads-bytes-from
For a
-
For each
ReadSharedMemory orReadModifyWriteSharedMemory event R inSharedDataBlockEventSet (execution), reads-bytes-from(R) in execution is aList of length R.[[ElementSize]] whose elements areWriteSharedMemory orReadModifyWriteSharedMemory events Ws such that all of the following are true.- Each event W with index i in Ws has R.[[ByteIndex]] + i in its range.
- R is not in Ws.
A
29.6.3 reads-from
For a
- For events R and W, R reads-from W in
execution if
SharedDataBlockEventSet (execution) contains both R and W, andreads-bytes-from (R) in execution contains W.
29.6.4 host-synchronizes-with
For a
- If E host-synchronizes-with D in execution,
HostEventSet (execution) contains E and D. - There is no cycle in the union of host-synchronizes-with and
is-agent-order-before in execution.
For two
29.6.5 synchronizes-with
For a
-
For events R and W, W synchronizes-with R in
execution if R
reads-from W in execution, R.[[Order]] isseq-cst , W.[[Order]] isseq-cst , and R and W have equal ranges. -
For each element eventsRecord of execution.[[EventsRecords]], the following is true.
- For events S and Sw, S synchronizes-with Sw in execution if eventsRecord.[[AgentSynchronizesWith]] contains (S, Sw).
- For events E and D, E synchronizes-with D in execution if execution.[[HostSynchronizesWith]] contains (E, D).
Owing to convention in
In a
In a
For
29.6.6 happens-before
For a
-
For events E and D, E happens-before D in execution if any of the following conditions are true.
- E
is-agent-order-before D in execution. - E
synchronizes-with D in execution. SharedDataBlockEventSet (execution) contains both E and D, E.[[Order]] isinit , and E and D have overlapping ranges.- There is an event F such that E happens-before F and F happens-before D in execution.
- E
Because happens-before is a superset of
29.7 Properties of Valid Executions
29.7.1 Valid Chosen Reads
A
- For each
ReadSharedMemory orReadModifyWriteSharedMemory event R ofSharedDataBlockEventSet (execution), do- Let chosenValueRecord be the element of execution.[[ChosenValues]] whose [[Event]] field is R.
- Let chosenValue be chosenValueRecord.[[ChosenValue]].
- Let readValue be
ValueOfReadEvent (execution, R). - Let chosenLen be the number of elements in chosenValue.
- Let readLen be the number of elements in readValue.
- If chosenLen ≠ readLen, then
- Return
false .
- Return
- If chosenValue[i] ≠ readValue[i] for
some
integer i in theinterval from 0 (inclusive) to chosenLen (exclusive), then- Return
false .
- Return
- Return
true .
29.7.2 Coherent Reads
A
- For each
ReadSharedMemory orReadModifyWriteSharedMemory event R ofSharedDataBlockEventSet (execution), do- Let Ws be
reads-bytes-from (R) in execution. - Let byteLocation be R.[[ByteIndex]].
- For each element W of Ws, do
- If R
happens-before W in execution, then- Return
false .
- Return
- If there exists a
WriteSharedMemory orReadModifyWriteSharedMemory event V that has byteLocation in its range such that Whappens-before V in execution and Vhappens-before R in execution, then- Return
false .
- Return
- Set byteLocation to byteLocation + 1.
- If R
- Let Ws be
- Return
true .
29.7.3 Tear Free Reads
A
- For each
ReadSharedMemory orReadModifyWriteSharedMemory event R ofSharedDataBlockEventSet (execution), do- If R.[[NoTear]] is
true , thenAssert : The remainder of dividing R.[[ByteIndex]] by R.[[ElementSize]] is 0.- For each event W such that R
reads-from W in execution and W.[[NoTear]] istrue , do- If R and W have equal ranges and there
exists an event V such that V and
W have equal ranges, V.[[NoTear]] is
true , W and V are not the sameShared Data Block event , and Rreads-from V in execution, then- Return
false .
- Return
- If R and W have equal ranges and there
exists an event V such that V and
W have equal ranges, V.[[NoTear]] is
- If R.[[NoTear]] is
- Return
true .
An event's [[NoTear]] field is
Intuitively, this requirement says when a memory range is accessed in an aligned fashion
via an
29.7.4 Sequentially Consistent Atomics
For a
- For events E and D, E is-memory-order-before D
in execution if E
happens-before D in execution. -
For events R and W such that R
reads-from W in execution, there is noWriteSharedMemory orReadModifyWriteSharedMemory event V inSharedDataBlockEventSet (execution) such that V.[[Order]] isseq-cst , W is-memory-order-before V in execution, V is-memory-order-before R in execution, and any of the following conditions are true.- W
synchronizes-with R in execution, and V and R have equal ranges. - W
happens-before R and Vhappens-before R in execution, W.[[Order]] isseq-cst , and W and V have equal ranges. - W
happens-before R and Whappens-before V in execution, R.[[Order]] isseq-cst , and V and R have equal ranges.
Note 1 This clause additionally constrains
seq-cst events on equal ranges. - W
-
For each
WriteSharedMemory orReadModifyWriteSharedMemory event W inSharedDataBlockEventSet (execution), if W.[[Order]] isseq-cst , then it is not the case that there is an infinite number ofReadSharedMemory orReadModifyWriteSharedMemory events inSharedDataBlockEventSet (execution) with equal range that is memory-order before W.Note 2
A
While is-memory-order-before includes all events in
29.7.5 Valid Executions
A
- The
host provides ahost-synchronizes-with Relation for execution. - execution admits a
happens-before Relation that is astrict partial order . - execution has valid chosen reads.
- execution has coherent reads.
- execution has tear free reads.
- execution has sequentially consistent atomics.
All programs have at least one valid execution.
29.8 Races
For an execution execution and events E and D that are contained in
- If E and D are not the same
Shared Data Block event , then- If it is not the case that both E
happens-before D in execution and Dhappens-before E in execution, then- If E and D are both
WriteSharedMemory orReadModifyWriteSharedMemory events and E and D do not have disjoint ranges, then- Return
true .
- Return
- If E
reads-from D in execution or Dreads-from E in execution, then- Return
true .
- Return
- If E and D are both
- If it is not the case that both E
- Return
false .
29.9 Data Races
For an execution execution and events E and D that are contained in
- If E and D are in a
race in execution, then- If E.[[Order]] is not
seq-cst or D.[[Order]] is notseq-cst , then- Return
true .
- Return
- If E and D have overlapping ranges, then
- Return
true .
- Return
- If E.[[Order]] is not
- Return
false .
29.10 Data Race Freedom
An execution execution is data race free if there are no two
events in
A program is data race free if all its executions are data race free.
The
29.11 Shared Memory Guidelines
The following are guidelines for ECMAScript programmers working with shared memory.
We recommend programs be kept
More generally, even if a program is not
The following are guidelines for ECMAScript implementers writing compiler transformations for programs using shared memory.
It is desirable to allow most program transformations that are valid in a single-
Let an agent-order slice be the subset
of the
Let possible read values of a read event be the set of all values of
Any transformation of an agent-order slice that is valid in the absence of shared memory is valid in the presence of shared memory, with the following exceptions.
-
Atomics are carved in stone: Program transformations must not cause the
seq-cst events in an agent-order slice to be reordered with itsunordered operations, nor itsseq-cst operations to be reordered with each other, nor may a program transformation remove aseq-cst operation from theis-agent-order-before Relation .(In practice, the prohibition on reorderings forces a compiler to assume that every
seq-cst operation is a synchronization and included in the finalis-memory-order-before Relation , which it would usually have to assume anyway in the absence of inter-agent program analysis. It also forces the compiler to assume that every call where the callee's effects on the memory-order are unknown may containseq-cst operations.) -
Reads must be stable: Any given shared memory read must only observe a single value in an execution.
(For example, if what is semantically a single read in the program is executed multiple times then the program is subsequently allowed to observe only one of the values read. A transformation known as rematerialization can violate this rule.)
-
Writes must be stable: All observable writes to shared memory must follow from program semantics in an execution.
(For example, a transformation may not introduce certain observable writes, such as by using read-modify-write operations on a larger location to write a smaller datum, writing a value to memory that the program could not have written, or writing a just-read value back to the location it was read from, if that location could have been overwritten by another
agent after the read.) -
Possible read values must be non-empty: Program transformations cannot cause the possible read values of a shared memory read to become empty.
(Counterintuitively, this rule in effect restricts transformations on writes, because writes have force in
memory model insofar as to be read by read events. For example, writes may be moved and coalesced and sometimes reordered between twoseq-cst operations, but the transformation may not remove every write that updates a location; some write must be preserved.)
Examples of transformations that remain valid are: merging multiple non-atomic reads from the
same location, reordering non-atomic reads, introducing speculative non-atomic reads,
merging multiple non-atomic writes to the same location, reordering non-atomic writes to
different locations, and hoisting non-atomic reads out of loops even if that affects
termination. Note in general that aliased
The following are guidelines for ECMAScript implementers generating machine code for shared memory accesses.
For architectures with memory models no weaker than those of ARM or Power, non-atomic stores
and loads may be compiled to bare stores and loads on the target architecture. Atomic stores
and loads may be compiled down to instructions that guarantee sequential consistency. If no
such instructions exist, memory barriers are to be employed, such as placing barriers on
both sides of a bare store or load. Read-modify-write operations may be compiled to
read-modify-write instructions on the target architecture, such as
LOCK-prefixed instructions on x86, load-exclusive/store-exclusive instructions
on ARM, and load-link/store-conditional instructions on Power.
Specifically, the
- Every atomic operation in the program is assumed to be necessary.
- Atomic operations are never rearranged with each other or with non-atomic operations.
- Functions are always assumed to perform atomic operations.
- Atomic operations are never implemented as read-modify-write operations on larger data, but as non-lock-free atomics if the platform does not have atomic operations of the appropriate size. (We already assume that every platform has normal memory access operations of every interesting size.)
Naive code generation uses these patterns:
- Regular loads and stores compile to single load and store instructions.
- Lock-free atomic loads and stores compile to a full (sequentially consistent) fence, a regular load or store, and a full fence.
- Lock-free atomic read-modify-write accesses compile to a full fence, an atomic read-modify-write instruction sequence, and a full fence.
- Non-lock-free atomics compile to a spinlock acquire, a full fence, a series of non-atomic load and store instructions, a full fence, and a spinlock release.
That mapping is correct so long as an atomic operation on an address range does not race with
a non-atomic write or with an atomic operation of different size. However, that is all we
need: the
Local improvements to those basic patterns are also allowed, subject to the constraints of
the
- There are obvious platform-dependent improvements that remove redundant fences. For
example, on x86 the fences around lock-free atomic loads and stores can always be
omitted except for the fence following a store, and no fence is needed for lock-free
read-modify-write instructions, as these all use
LOCK-prefixed instructions. On many platforms there are fences of several strengths, and weaker fences can be used in certain contexts without destroying sequential consistency. - Most modern platforms support lock-free atomics for all the data sizes required by ECMAScript atomics. Should non-lock-free atomics be needed, the fences surrounding the body of the atomic operation can usually be folded into the lock and unlock steps. The simplest solution for non-lock-free atomics is to have a single lock word per SharedArrayBuffer.
- There are also more complicated platform-dependent local improvements, requiring some code analysis. For example, two back-to-back fences often have the same effect as a single fence, so if code is generated for two atomic operations in sequence, only a single fence need separate them. On x86, even a single fence separating atomic stores can be omitted, as the fence following a store is only needed to separate the store from a subsequent load.
Annex A (informative) Grammar Summary
A.1 Lexical Grammar
A.2 Expressions
When processing an instance of the production
the interpretation of
When processing an instance of the production
the interpretation of
In certain circumstances when processing an instance of the production
the interpretation of
A.3 Statements
A.4 Functions and Classes
When processing an instance of the production
the interpretation of
When processing an instance of the production
the interpretation of
A.5 Scripts and Modules
A.6 Number Conversions
All grammar symbols not explicitly defined by the
A.7 Time Zone Offset String Format
A.8 Regular Expressions
Each \u u u \u
Annex B (normative) Additional ECMAScript Features for Web Browsers
The ECMAScript language syntax and semantics defined in this annex are required when the ECMAScript
This annex describes various legacy features and other characteristics of web browser ECMAScript
These features are not considered part of the core ECMAScript language. Programmers should not use or assume the existence of these features and behaviours when writing new ECMAScript code. ECMAScript implementations are discouraged from implementing these features unless the implementation is part of a web browser or is required to run the same legacy ECMAScript code that web browsers encounter.
B.1 Additional Syntax
B.1.1 HTML-like Comments
The syntax and semantics of
Syntax
Similar to a
B.1.2 Regular Expressions Patterns
The syntax of
This alternative pattern grammar and semantics only changes the syntax and semantics of BMP
patterns. The following grammar extensions include productions parameterized with the
[UnicodeMode] parameter. However, none of these extensions change the syntax of Unicode patterns
recognized when parsing with the [UnicodeMode] parameter present on the
Syntax
When the same left-hand sides occurs with both [+UnicodeMode] and [~UnicodeMode] guards it is to control the disambiguation priority.
B.1.2.1 Static Semantics: Early Errors
The semantics of
- It is a Syntax Error if any source text is matched by this production.
Additionally, the rules for the following productions are modified with the addition of the highlighted text:
-
It is a Syntax Error if
IsCharacterClass of the firstClassAtom istrue orIsCharacterClass of the secondClassAtom istrue and this production has a [UnicodeMode] parameter. -
It is a Syntax Error if
IsCharacterClass of the firstClassAtom isfalse ,IsCharacterClass of the secondClassAtom isfalse , and theCharacterValue of the firstClassAtom is strictly greater than theCharacterValue of the secondClassAtom .
-
It is a Syntax Error if
IsCharacterClass ofClassAtomNoDash istrue orIsCharacterClass ofClassAtom istrue and this production has a [UnicodeMode] parameter. -
It is a Syntax Error if
IsCharacterClass ofClassAtomNoDash isfalse ,IsCharacterClass ofClassAtom isfalse , and theCharacterValue ofClassAtomNoDash is strictly greater than theCharacterValue ofClassAtom .
B.1.2.2 Static Semantics: CountLeftCapturingParensWithin and CountLeftCapturingParensBefore
In the definitions of
B.1.2.3 Static Semantics: IsCharacterClass
The semantics of
- Return
false .
B.1.2.4 Static Semantics: CharacterValue
The semantics of
- Return the numeric value of U+005C (REVERSE SOLIDUS).
- Let ch be the code point matched by
ClassControlLetter . - Let i be the numeric value of ch.
- Return the remainder of dividing i by 32.
- Return the MV of
LegacyOctalEscapeSequence (see12.9.4.3 ).
B.1.2.5 Runtime Semantics: CompileSubpattern
The semantics of
The rule for
The rule for
The rule for
B.1.2.6 Runtime Semantics: CompileAssertion
B.1.2.7 Runtime Semantics: CompileAtom
- Let A be the
CharSet containing the single character\U+005C (REVERSE SOLIDUS). - Return
CharacterSetMatcher (rer, A,false , direction).
- Let ch be the character represented by
ExtendedPatternCharacter . - Let A be a one-element
CharSet containing the character ch. - Return
CharacterSetMatcher (rer, A,false , direction).
B.1.2.8 Runtime Semantics: CompileToCharSet
The semantics of
The following two rules replace the corresponding rules of
- Let A be
CompileToCharSet of the firstClassAtom with argument rer. - Let B be
CompileToCharSet of the secondClassAtom with argument rer. - Let C be
CompileToCharSet ofClassContents with argument rer. - Let D be
CharacterRangeOrUnion (rer, A, B). - Return the union of D and C.
- Let A be
CompileToCharSet ofClassAtomNoDash with argument rer. - Let B be
CompileToCharSet ofClassAtom with argument rer. - Let C be
CompileToCharSet ofClassContents with argument rer. - Let D be
CharacterRangeOrUnion (rer, A, B). - Return the union of D and C.
In addition, the following rules are added to
- Let cv be the
CharacterValue of thisClassEscape . - Let c be the character whose character value is cv.
- Return the
CharSet containing the single character c.
- Return the
CharSet containing the single character\U+005C (REVERSE SOLIDUS).
\c within a character class where it is not followed by an acceptable
control character.
B.1.2.8.1 CharacterRangeOrUnion ( rer, A, B )
The abstract operation CharacterRangeOrUnion takes arguments rer (a
- If
HasEitherUnicodeFlag (rer) isfalse , then - Return
CharacterRange (A, B).
B.1.2.9 Static Semantics: ParsePattern ( patternText, u, v )
The semantics of
The abstract operation
- If v is
true and u istrue , then- Let parseResult be a
List containing one or moreSyntaxError objects.
- Let parseResult be a
- Else if v is
true , then - Else if u is
true , then - Else,
- Return parseResult.
B.2 Additional Built-in Properties
When the ECMAScript
B.2.1 Additional Properties of the Global Object
The entries in
| Intrinsic Name | Global Name | ECMAScript Language Association |
|---|---|---|
|
|
escape
|
The escape function ( |
|
|
unescape
|
The unescape function ( |
B.2.1.1 escape ( string )
This function is a property of the
When replacing a code unit of numeric value less than or equal to 0x00FF, a two-digit escape
sequence of the form %xx is used. When replacing a code unit of
numeric value strictly greater than 0x00FF, a four-digit escape sequence of the form
%uxxxx is used.
It is the %escape% intrinsic object.
It performs the following steps when called:
- Set string to ?
ToString (string). - Let len be the length of string.
- Let R be the empty String.
- Let unescapedSet be the
string-concatenation ofthe ASCII word characters and"@*+-./" . - Let k be 0.
- Repeat, while k < len,
- Let C be the code unit at index k within string.
- If unescapedSet contains C, then
- Let S be C.
- Else,
- Let n be the numeric value of C.
- If n < 256, then
- Let hex be the String representation of n, formatted as an uppercase hexadecimal number.
- Let S be the
string-concatenation of"%" andStringPad (hex, 2,"0" ,start ).
- Else,
- Let hex be the String representation of n, formatted as an uppercase hexadecimal number.
- Let S be the
string-concatenation of"%u" andStringPad (hex, 4,"0" ,start ).
- Set R to the
string-concatenation of R and S. - Set k to k + 1.
- Return R.
The encoding is partly based on the encoding described in RFC 1738, but the entire encoding specified in this standard is described above without regard to the contents of RFC 1738. This encoding does not reflect changes to RFC 1738 made by RFC 3986.
B.2.1.2 unescape ( string )
This function is a property of the escape function is replaced with the code unit that it represents.
It is the %unescape% intrinsic object.
It performs the following steps when called:
- Set string to ?
ToString (string). - Let len be the length of string.
- Let R be the empty String.
- Let k be 0.
- Repeat, while k < len,
- Let C be the code unit at index k within string.
- If C is the code unit 0x0025 (PERCENT SIGN), then
- Let hexDigits be the empty String.
- Let optionalAdvance be 0.
- If k + 5 < len and the code unit at index
k + 1 within string is the code unit 0x0075
(LATIN SMALL LETTER U), then
- Set hexDigits to the
substring of string from k + 2 to k + 6. - Set optionalAdvance to 5.
- Set hexDigits to the
- Else if k + 3 ≤ len, then
- Set hexDigits to the
substring of string from k + 1 to k + 3. - Set optionalAdvance to 2.
- Set hexDigits to the
- Let parseResult be
ParseText (hexDigits,HexDigits ).[~Sep] - If parseResult is a
Parse Node , then- Let n be the MV of parseResult.
- Set C to the code unit whose numeric value is n.
- Set k to k + optionalAdvance.
- Set R to the
string-concatenation of R and C. - Set k to k + 1.
- Return R.
B.2.2 Additional Properties of the String.prototype Object
B.2.2.1 String.prototype.substr ( start, length )
This method returns a
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let size be the length of S.
- Let intStart be ?
ToIntegerOrInfinity (start). - If intStart = -∞, set intStart to 0.
- Else if intStart < 0, set intStart to
max (size + intStart, 0). - Else, set intStart to
min (intStart, size). - If length is
undefined , let intLength be size; otherwise let intLength be ?ToIntegerOrInfinity (length). - Set intLength to the result of
clamping intLength between 0 and size. - Let intEnd be
min (intStart + intLength, size). - Return the
substring of S from intStart to intEnd.
This method is intentionally generic; it does not require that its
B.2.2.2 String.prototype.anchor ( name )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"a" ,"name" , name).
B.2.2.2.1 CreateHTML ( string, tag, attribute, value )
The abstract operation CreateHTML takes arguments string (an
- Let str be ?
RequireObjectCoercible (string). - Let S be ?
ToString (str). - Let p1 be the
string-concatenation of"<" and tag. - If attribute is not the empty String, then
- Let V be ?
ToString (value). - Let escapedV be the String value that is the same as
V except that each occurrence of the code unit 0x0022
(QUOTATION MARK) in V has been replaced with the six code
unit sequence
""" . - Set p1 to the
string-concatenation of:- p1
- the code unit 0x0020 (SPACE)
- attribute
- the code unit 0x003D (EQUALS SIGN)
- the code unit 0x0022 (QUOTATION MARK)
- escapedV
- the code unit 0x0022 (QUOTATION MARK)
- Let V be ?
- Let p2 be the
string-concatenation of p1 and">" . - Let p3 be the
string-concatenation of p2 and S. - Let p4 be the
string-concatenation of p3,"</" , tag, and">" . - Return p4.
B.2.2.3 String.prototype.big ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"big" ,"" ,"" ).
B.2.2.4 String.prototype.blink ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"blink" ,"" ,"" ).
B.2.2.5 String.prototype.bold ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"b" ,"" ,"" ).
B.2.2.6 String.prototype.fixed ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"tt" ,"" ,"" ).
B.2.2.7 String.prototype.fontcolor ( colour )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"font" ,"color" , colour).
B.2.2.8 String.prototype.fontsize ( size )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"font" ,"size" , size).
B.2.2.9 String.prototype.italics ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"i" ,"" ,"" ).
B.2.2.10 String.prototype.link ( url )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"a" ,"href" , url).
B.2.2.11 String.prototype.small ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"small" ,"" ,"" ).
B.2.2.12 String.prototype.strike ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"strike" ,"" ,"" ).
B.2.2.13 String.prototype.sub ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"sub" ,"" ,"" ).
B.2.2.14 String.prototype.sup ( )
This method performs the following steps when called:
- Let S be the
this value. - Return ?
CreateHTML (S,"sup" ,"" ,"" ).
B.2.2.15 String.prototype.trimLeft ( )
The property
The initial value of the
B.2.2.16 String.prototype.trimRight ( )
The property
The initial value of the
B.2.3 Additional Properties of the Date.prototype Object
B.2.3.1 Date.prototype.getYear ( )
The getFullYear method is preferred for nearly all purposes, because it
avoids the “year 2000 problem.”
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
YearFromTime (LocalTime (t)) -1900 𝔽.
B.2.3.2 Date.prototype.setYear ( year )
The setFullYear method is preferred for nearly all purposes, because it
avoids the “year 2000 problem.”
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let y be ?
ToNumber (year). - If t is
NaN , set t to+0 𝔽; otherwise set t toLocalTime (t). - Let yyyy be
MakeFullYear (y). - Let d be
MakeDay (yyyy,MonthFromTime (t),DateFromTime (t)). - Let date be
MakeDate (d,TimeWithinDay (t)). - Let u be
TimeClip (UTC (date)). - Set dateObject.[[DateValue]] to u.
- Return u.
B.2.3.3 Date.prototype.toGMTString ( )
The toUTCString method is preferred. This method is provided principally
for compatibility with old code.
The initial value of the
B.2.4 Additional Properties of the RegExp.prototype Object
B.2.4.1 RegExp.prototype.compile ( pattern, flags )
This method performs the following steps when called:
- Let O be the
this value. - Perform ?
RequireInternalSlot (O, [[RegExpMatcher]]). - If pattern
is an Object and pattern has a [[RegExpMatcher]] internal slot, then- If flags is not
undefined , throw aTypeError exception. - Let P be pattern.[[OriginalSource]].
- Let F be pattern.[[OriginalFlags]].
- If flags is not
- Else,
- Let P be pattern.
- Let F be flags.
- Return ?
RegExpInitialize (O, P, F).
This method completely reinitializes the
B.3 Other Additional Features
B.3.1 Labelled Function Declarations
Prior to ECMAScript 2015, the specification of
-
It is a Syntax Error if any source text that is
strict mode code is matched by this production.
The
B.3.2 Block-Level Function Declarations Web Legacy Compatibility Semantics
Prior to ECMAScript 2015, the ECMAScript specification did not define the occurrence of a
-
A function is declared and only referenced within a single block.
-
One or more
FunctionDeclaration s whoseBindingIdentifier is the name f occur within the function code of an enclosing function g and that declaration is nested within aBlock . -
No other declaration of f that is not a
vardeclaration occurs within the function code of g. -
All occurrences of f as an
IdentifierReference are within theStatementList of theBlock containing the declaration of f.
-
One or more
-
A function is declared and possibly used within a single
Block but also referenced by an inner function definition that is not contained within that sameBlock .-
One or more
FunctionDeclaration s whoseBindingIdentifier is the name f occur within the function code of an enclosing function g and that declaration is nested within aBlock . -
No other declaration of f that is not a
vardeclaration occurs within the function code of g. -
There may be occurrences of f as an
IdentifierReference within theStatementList of theBlock containing the declaration of f. -
There is at least one occurrence of f as an
IdentifierReference within another function h that is nested within g and no other declaration of f shadows the references to f from within h. - All invocations of h occur after the declaration of f has been evaluated.
-
One or more
-
A function is declared and possibly used within a single block but also referenced within subsequent blocks.
-
One or more
FunctionDeclaration whoseBindingIdentifier is the name f occur within the function code of an enclosing function g and that declaration is nested within aBlock . -
No other declaration of f that is not a
vardeclaration occurs within the function code of g. -
There may be occurrences of f as an
IdentifierReference within theStatementList of theBlock containing the declaration of f. -
There is at least one occurrence of f as an
IdentifierReference within the function code of g that lexically follows theBlock containing the declaration of f.
-
One or more
The first use case is interoperable with the semantics of
ECMAScript 2015 interoperability for the second and third use cases requires the following
extensions to the clause
If an ECMAScript implementation has a mechanism for reporting diagnostic warning messages, a
warning should be produced when code contains a
B.3.2.1 Changes to FunctionDeclarationInstantiation
During
- If strict is
false , then- For each
FunctionDeclaration f that is directly contained in theStatementList of anyBlock ,CaseClause , orDefaultClause x such that codeContains x istrue , do- Let F be the
StringValue of theBindingIdentifier of f. - If replacing the
FunctionDeclaration f with aVariableStatement that has F as aBindingIdentifier would not produce any Early Errors for func and parameterNames does not contain F, then- NOTE: A var binding for F is only instantiated
here if it is neither a VarDeclaredName, the name of a
formal parameter, or another
FunctionDeclaration . - If instantiatedVarNames does not contain
F and F is not
"arguments" , then- Perform
! varEnv.CreateMutableBinding(F,
false ). - Perform
! varEnv.InitializeBinding(F,
undefined ). - Append F to instantiatedVarNames.
- Perform
! varEnv.CreateMutableBinding(F,
- When the
FunctionDeclaration f is evaluated, perform the following steps in place of theFunctionDeclaration Evaluation algorithm provided in15.2.6 :- Let fEnv be the
running execution context 's VariableEnvironment. - Let bEnv be the
running execution context 's LexicalEnvironment. - Let fObj be
! bEnv.GetBindingValue(F,
false ). - Perform
! fEnv.SetMutableBinding(F,
fObj,
false ). - Return
unused .
- Let fEnv be the
- NOTE: A var binding for F is only instantiated
here if it is neither a VarDeclaredName, the name of a
formal parameter, or another
- Let F be the
- For each
B.3.2.2 Changes to GlobalDeclarationInstantiation
During
- Perform the following steps:
- Let strict be
ScriptIsStrict of script. - If strict is
false , then- Let declaredFunctionOrVarNames be the
list-concatenation of declaredFunctionNames and declaredVarNames. - For each
FunctionDeclaration f that is directly contained in theStatementList of anyBlock ,CaseClause , orDefaultClause x such that scriptContains x istrue , do- Let F be the
StringValue of theBindingIdentifier of f. - If replacing the
FunctionDeclaration f with aVariableStatement that has F as aBindingIdentifier would not produce any Early Errors for script, then- If
HasLexicalDeclaration (env, F) isfalse , then- Let fnDefinable be
?
CanDeclareGlobalVar (env, F). - If fnDefinable is
true , then- NOTE: A var binding for F
is only instantiated here if it is
neither a VarDeclaredName nor the
name of another
FunctionDeclaration . - If
declaredFunctionOrVarNames
does not contain F, then
- Perform ?
CreateGlobalVarBinding (env, F,false ). - Append F to declaredFunctionOrVarNames.
- Perform ?
- When the
FunctionDeclaration f is evaluated, perform the following steps in place of theFunctionDeclaration Evaluation algorithm provided in15.2.6 :- Let gEnv be the
running execution context 's VariableEnvironment. - Let bEnv be the
running execution context 's LexicalEnvironment. - Let fObj be
! bEnv.GetBindingValue(F,
false ). - Perform ? gEnv.SetMutableBinding(F,
fObj,
false ). - Return
unused .
- Let gEnv be the
- NOTE: A var binding for F
is only instantiated here if it is
neither a VarDeclaredName nor the
name of another
- Let fnDefinable be
?
- If
- Let F be the
- Let declaredFunctionOrVarNames be the
- Let strict be
B.3.2.3 Changes to EvalDeclarationInstantiation
During
- If strict is
false , then- Let declaredFunctionOrVarNames be the
list-concatenation of declaredFunctionNames and declaredVarNames. - For each
FunctionDeclaration f that is directly contained in theStatementList of anyBlock ,CaseClause , orDefaultClause x such that bodyContains x istrue , do- Let F be the
StringValue of theBindingIdentifier of f. - If replacing the
FunctionDeclaration f with aVariableStatement that has F as aBindingIdentifier would not produce any Early Errors for body, then- Let bindingExists be
false . - Let thisEnv be lexEnv.
Assert : The following loop will terminate.- Repeat, while thisEnv is not varEnv,
- If thisEnv
is not an Object Environment Record , then- If
! thisEnv.HasBinding(F)
is
true , then-
Let bindingExists be
true .
-
Let bindingExists be
- If
! thisEnv.HasBinding(F)
is
- Set thisEnv to thisEnv.[[OuterEnv]].
- If thisEnv
- If bindingExists is
false and varEnv is aGlobal Environment Record , then- If
HasLexicalDeclaration (varEnv, F) isfalse , then- Let fnDefinable be
?
CanDeclareGlobalVar (varEnv, F).
- Let fnDefinable be
?
- Else,
- Let fnDefinable be
false .
- Let fnDefinable be
- If
- Else,
- Let fnDefinable be
true .
- Let fnDefinable be
- If bindingExists is
false and fnDefinable istrue , then- If declaredFunctionOrVarNames does not
contain F, then
- If varEnv is a
Global Environment Record , then- Perform ?
CreateGlobalVarBinding (varEnv, F,true ).
- Perform ?
- Else,
- Let bindingExists be ! varEnv.HasBinding(F).
- If bindingExists is
false , then- Perform
! varEnv.CreateMutableBinding(F,
true ). - Perform
! varEnv.InitializeBinding(F,
undefined ).
- Perform
! varEnv.CreateMutableBinding(F,
- Append F to declaredFunctionOrVarNames.
- If varEnv is a
- When the
FunctionDeclaration f is evaluated, perform the following steps in place of theFunctionDeclaration Evaluation algorithm provided in15.2.6 :- Let gEnv be the
running execution context 's VariableEnvironment. - Let bEnv be the
running execution context 's LexicalEnvironment. - Let fObj be
! bEnv.GetBindingValue(F,
false ). - Perform ? gEnv.SetMutableBinding(F,
fObj,
false ). - Return
unused .
- Let gEnv be the
- If declaredFunctionOrVarNames does not
contain F, then
- Let bindingExists be
- Let F be the
- Let declaredFunctionOrVarNames be the
B.3.2.4 Changes to Block Static Semantics: Early Errors
The rules for the following production in
-
It is a Syntax Error if the
LexicallyDeclaredNames ofStatementList contains any duplicate entries, unlessIsStrict (this production) isfalse and the duplicate entries are only bound by FunctionDeclarations. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofStatementList also occurs in theVarDeclaredNames ofStatementList .
B.3.2.5 Changes to switch Statement Static
Semantics: Early Errors
The rules for the following production in
-
It is a Syntax Error if the
LexicallyDeclaredNames ofCaseBlock contains any duplicate entries, unlessIsStrict (this production) isfalse and the duplicate entries are only bound by FunctionDeclarations. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofCaseBlock also occurs in theVarDeclaredNames ofCaseBlock .
B.3.2.6 Changes to BlockDeclarationInstantiation
During
- If ! env.HasBinding(dn) is
false , then- Perform ! env.CreateMutableBinding(dn,
false ).
- Perform ! env.CreateMutableBinding(dn,
During
- Perform the following steps:
- If the binding for fn in env is an uninitialized
binding, then
- Perform ! env.InitializeBinding(fn, fo).
- Else,
Assert : d is aFunctionDeclaration .- Perform ! env.SetMutableBinding(fn,
fo,
false ).
- If the binding for fn in env is an uninitialized
binding, then
B.3.3 FunctionDeclarations in IfStatement Statement Clauses
The following augments the
This production only applies when parsing
B.3.4 VariableStatements in Catch Blocks
The content of subclause
-
It is a Syntax Error if the
BoundNames ofCatchParameter contains any duplicate elements. -
It is a Syntax Error if any element of the
BoundNames ofCatchParameter also occurs in theLexicallyDeclaredNames ofBlock . -
It is a Syntax Error if any element of the
BoundNames ofCatchParameter also occurs in theVarDeclaredNames ofBlock unlessCatchParameter isCatchParameter : BindingIdentifier
The var declarations that bind a name that is also bound by the var declarations will assign to the corresponding catch parameter rather
than the var binding.
This modified behaviour also applies to var and function declarations
introduced by
Step
- If thisEnv is not the
Environment Record for aCatch clause, throw aSyntaxError exception.
Step
- If thisEnv is not the
Environment Record for aCatch clause, let bindingExists betrue .
B.3.5 Initializers in ForIn Statement Heads
The following augments the
This production only applies when parsing
The
- Return
ContainsDuplicateLabels ofStatement with argument labelSet.
The
- Return
ContainsUndefinedBreakTarget ofStatement with argument labelSet.
The
- Return
ContainsUndefinedContinueTarget ofStatement with arguments iterationSet and « ».
The
- Return
false .
The
- Let names1 be the
BoundNames ofBindingIdentifier . - Let names2 be the
VarDeclaredNames ofStatement . - Return the
list-concatenation of names1 and names2.
The
- Let declarations1 be «
BindingIdentifier ». - Let declarations2 be the
VarScopedDeclarations ofStatement . - Return the
list-concatenation of declarations1 and declarations2.
The
- Let bindingId be the
StringValue ofBindingIdentifier . - Let lhs be ?
ResolveBinding (bindingId). - If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Let value be ?
NamedEvaluation ofInitializer with argument bindingId.
- Let value be ?
- Else,
- Let rhs be ?
Evaluation ofInitializer . - Let value be ?
GetValue (rhs).
- Let rhs be ?
- Perform ?
PutValue (lhs, value). - Let keyResult be ?
ForIn/OfHeadEvaluation (« »,Expression ,enumerate ). - Return ?
ForIn/OfBodyEvaluation (BindingIdentifier ,Statement , keyResult,enumerate ,var-binding , labelSet).
B.3.6 The [[IsHTMLDDA]] Internal Slot
An [[IsHTMLDDA]] internal slot may exist on
typeof operator
Objects with an [[IsHTMLDDA]] internal slot are never created by
this specification. However, the document.all
object in web browsers is a document.all.
B.3.6.1 Changes to ToBoolean
The following step replaces step
- If argument
is an Object and argument has an [[IsHTMLDDA]] internal slot, returnfalse .
B.3.6.2 Changes to IsLooselyEqual
The following steps replace step
- Perform the following steps:
- If x
is an Object , x has an [[IsHTMLDDA]] internal slot, and y is eitherundefined ornull , returntrue . - If x is either
undefined ornull , yis an Object , and y has an [[IsHTMLDDA]] internal slot, returntrue .
- If x
B.3.6.3 Changes to the typeof Operator
The following step replaces step typeof
- If val has an [[IsHTMLDDA]] internal slot,
return
"undefined" .
B.3.7 Non-default behaviour in HostMakeJobCallback
The
B.3.8 Non-default behaviour in HostEnsureCanAddPrivateElement
The
B.3.9 Runtime Errors for Function Call Assignment Targets
When a function call (
When the assignment target is the = or an ??=,
&&=, ||=).
See step
Annex C (informative) The Strict Mode of ECMAScript
The strict mode restriction and exceptions
-
implements,interface,let,package,private,protected,public,static, andyieldarereserved words withinstrict mode code . (12.7.2 ). -
A conforming implementation, when processing
strict mode code , must disallow instances of the productionsNumericLiteral :: LegacyOctalIntegerLiteral DecimalIntegerLiteral :: NonOctalDecimalIntegerLiteral -
A conforming implementation, when processing
strict mode code , must disallow instances of the productionsEscapeSequence :: LegacyOctalEscapeSequence EscapeSequence :: NonOctalDecimalEscapeSequence -
Assignment to an undeclared identifier or otherwise unresolvable reference does not create a
property in the
global object . When a simple assignment occurs withinstrict mode code , itsLeftHandSideExpression must not evaluate to an unresolvable Reference. If it does aReferenceError exception is thrown (6.2.5.6 ). TheLeftHandSideExpression also may not be a reference to adata property with the attribute value { [[Writable]]:false }, to anaccessor property with the attribute value { [[Set]]:undefined }, nor to a non-existent property of an object whose [[Extensible]] internal slot isfalse . In these cases aTypeErrorexception is thrown (13.15 ). -
An
IdentifierReference with theStringValue "eval" or"arguments" may not appear as theLeftHandSideExpression of an Assignment operator (13.15 ) or of anUpdateExpression (13.4 ) or as theUnaryExpression operated upon by a Prefix Increment (13.4.4 ) or a Prefix Decrement (13.4.5 ) operator. -
Arguments objects for
strict functions define a non-configurableaccessor property "callee" which throws aTypeError exception on access (10.4.4.6 ). -
Arguments objects for
strict functions do not dynamically share theirarray-indexed property values with the corresponding formal parameter bindings of their functions. (10.4.4 ). -
For
strict functions , if an arguments object is created the binding of the local identifierargumentsto the arguments object is immutable and hence may not be the target of an assignment expression. (10.2.11 ). -
It is a
SyntaxError if theStringValue of aBindingIdentifier is either"eval" or"arguments" withinstrict mode code (13.1.1 ). -
Strict mode eval code cannot instantiate variables or functions in the variable environment of the
caller to eval. Instead, a new variable environment is created and that environment is used for
declaration binding instantiation for the eval code (
19.2.1 ). -
If
this is evaluated withinstrict mode code , then thethis value is not coerced to an object. Athis value of eitherundefined ornull is not converted to theglobal object and primitive values are not converted to wrapper objects. Thethis value passed via a function call (including calls made usingFunction.prototype.applyandFunction.prototype.call) do not coerce the passedthis value to an object (10.2.1.2 ,20.2.3.1 ,20.2.3.3 ). -
When a
deleteoperator occurs withinstrict mode code , aSyntaxError is thrown if itsUnaryExpression is a direct reference to a variable, function argument, or function name (13.5.1.1 ). -
When a
deleteoperator occurs withinstrict mode code , aTypeError is thrown if the property to be deleted has the attribute { [[Configurable]]:false } or otherwise cannot be deleted (13.5.1.2 ). -
Strict mode code may not include aWithStatement . The occurrence of aWithStatement in such a context is aSyntaxError (14.11.1 ). -
It is a
SyntaxError if aCatchParameter occurs withinstrict mode code and theBoundNames ofCatchParameter contains eitherevalorarguments(14.15.1 ). -
It is a
SyntaxError if the sameBindingIdentifier appears more than once in theFormalParameters of astrict function . An attempt to create such a function using a Function, Generator, or AsyncFunctionconstructor is aSyntaxError (15.2.1 ,20.2.1.1.1 ). -
An implementation may not extend, beyond that defined in this specification, the meanings within
strict functions of properties named"caller" or"arguments" of function instances.
Annex D (informative) Host Layering Points
See
D.1 Host Hooks
D.2 Host-defined Fields
[[HostDefined]] on
[[HostDefined]] on
[[HostDefined]] on
[[HostDefined]] on
[[HostSynchronizesWith]] on Candidate Executions: See
[[IsHTMLDDA]]: See
D.3 Host-defined Objects
The
D.4 Running Jobs
Preparation steps before, and cleanup steps after, invocation of
D.5 Internal Methods of Exotic Objects
Any of the essential internal methods in
D.6 Built-in Objects and Methods
Any built-in objects and methods not defined within this specification, except as restricted in
Annex E (informative) Corrections and Clarifications in ECMAScript 2015 with Possible Compatibility Impact
Date.prototype.toString when the
/.
String.prototype.match and String.prototype.replace was
incorrect for cases where the pattern argument was a RegExp value whose global flag is set.
The previous specifications stated that for each attempt to match the pattern, if lastIndex
did not change, it should be incremented by 1. The correct behaviour is that lastIndex
should be incremented by 1 only if the pattern matched the empty String.
Array.prototype.sort. ECMAScript 2015 specifies that such as value is treated as if
Annex F (informative) Additions and Changes That Introduce Incompatibilities with Prior Editions
Space_Separator (Zs) category and thus treated as whitespace in ECMAScript
2015, to be moved to the Format (Cf) category (as of Unicode 6.3.0). This
causes whitespace-sensitive methods to behave differently. For example,
"\u180E".trim().length was 0 in previous editions, but 1 in
ECMAScript 2016 and later. Additionally, ECMAScript 2017 mandated always using the latest version of the
Unicode Standard.
let followed by the token [ is the start of a
(
token of a for statement is immediately followed by the token sequence let [ then the
let is treated as the start of a
let [ then the
let is treated as the start of a
in
var declaration for the same
eval
whose eval code includes a var or FunctionDeclaration declaration that binds
the same
Object.freeze is not an object it is treated as if
it was a non-extensible
Object.getOwnPropertyDescriptor is not an object an attempt is made to coerce
the argument using
Object.getOwnPropertyNames is not an object an attempt is made to coerce the
argument using
Object.getPrototypeOf is not an object an attempt is made to coerce the argument using
Object.isExtensible is not an object it is treated as if it was a non-extensible
Object.isFrozen is not an object it is treated as if it was a non-extensible
Object.isSealed is not an object it is treated as if it was a non-extensible
Object.keys is not an object an attempt is made to
coerce the argument using
Object.preventExtensions is not an object it is treated as if it was a
non-extensible
Object.seal is not an object it is treated as if it was
a non-extensible
String.prototype.localeCompare function must treat Strings that are canonically equivalent
according to the Unicode Standard as being identical. In previous editions implementations were
permitted to ignore canonical equivalence and could instead use a bit-wise comparison.
String.prototype.trim method is defined to recognize white space code points that may exist
outside of the Unicode BMP. However, as of Unicode 7 no such code points are defined. In previous
editions such code points would not have been recognized as white space.
Atomics.wake has been renamed to Atomics.notify to prevent
confusion with Atomics.wait.
await
was reduced, which could create an observable difference in resolution order between a
then() call and an await expression.
Bibliography
-
IEEE 754-2019: IEEE Standard for Floating-Point Arithmetic.
Institute of Electrical and Electronic Engineers, New York (2019)
Note There are no normative changes between IEEE 754-2008 and IEEE 754-2019 that affect the ECMA-262 specification.
- The Unicode Standard, available at <https://unicode.org/versions/latest>
- Unicode Technical Note #5: Canonical Equivalence in Applications, available at <https://unicode.org/notes/tn5/>
- Unicode Technical Standard #10: Unicode Collation Algorithm, available at <https://unicode.org/reports/tr10/>
- Unicode Standard Annex #15, Unicode Normalization Forms, available at <https://unicode.org/reports/tr15/>
- Unicode Standard Annex #18: Unicode Regular Expressions, available at <https://unicode.org/reports/tr18/>
-
Unicode Standard Annex #24: Unicode
ScriptProperty, available at <https://unicode.org/reports/tr24/> - Unicode Standard Annex #31, Unicode Identifiers and Pattern Syntax, available at <https://unicode.org/reports/tr31/>
- Unicode Standard Annex #44: Unicode Character Database, available at <https://unicode.org/reports/tr44/>
- Unicode Technical Standard #51: Unicode Emoji, available at <https://unicode.org/reports/tr51/>
- IANA Time Zone Database, available at <https://www.iana.org/time-zones>
- ISO 8601:2004(E) Data elements and interchange formats — Information interchange — Representation of dates and times
- RFC 1738 “Uniform Resource Locators (URL)”, available at <https://tools.ietf.org/html/rfc1738>
- RFC 2396 “Uniform Resource Identifiers (URI): Generic Syntax”, available at <https://tools.ietf.org/html/rfc2396>
- RFC 3629 “UTF-8, a transformation format of ISO 10646”, available at <https://tools.ietf.org/html/rfc3629>
- RFC 7231 “Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content”, available at <https://tools.ietf.org/html/rfc7231>
Colophon
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